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All Textbook Solutions for Organic Chemistry

1.1P 1.2P Judging from their relative positions in the Periodic Table, which element in each set is more electronegative? (a) Lithium or carbon (b) Nitrogen or oxygen (c) Carbon or oxygen Classify each bond as nonpolar covalent or polar covalent or state that ions are formed. (a) SH (b) PH (c) CF (d) CCl Using the symbols and +, indicate the direction of polarity in each polar covalent bond. (a) CN (b) NO (c) CCl Draw Lewis structures showing all valence electrons for these molecules. (a) C2H6 (b) CS2 (c) HCN Draw Lewis structures for these ions and show which atom (or atoms) in each bears the formal charge. (a) CH3NH3+ (b) CO32 (c) OH Draw Lewis structures and condensed structural formulas for the four alcohols with the molecular formula C4H10O. Classify each alcohol as primary, secondary, or tertiary.1.9P 1.10P 1.11P 1.12P Predict all bond angles for these molecules. (a) CH3OH (b) PF3 (c) H2CO3 The geometry of carbon in diamond is tetrahedral, while carbons geometry in graphite is trigonal planar. What is the geometry of the carbons in C60? 1. They are all tetrahedral. 2. They are all trigonal planar. 3. They are all pyramidal with bond angles near 109.5. 4. They are not perfectly trigonal planar but have an extent of pyramidalization.Because of their spherical shape, C60 molecules are used as nanoscale ball bearings in grease and lubricants. We can estimate the size of these ball bearings by examining CC bond distances. Carbon-carbon bond distances vary between approximately 120 pm (pm = picometers) and 155 pm. What is the approximate diameter of C60? 1. 10 pm 2. 100 pm 3. 1000 pm 4. 10,000 pm What best describes the CCC bond angles in C60? 1. They are exactly 120. 2. They are a bit larger than 120. 3. They are a bit smaller than 120. 4. They are near 109.5.1.14P Describe the bonding in these molecules in terms of hybridization of C and N and the types of bonds between carbon and nitrogen. If there are any lone pairs, describe what type of orbital contains these electrons. (a) CH3CH=CH2 (b) CH3NH2 1.16P 1.17P 1.18P Draw three contributing structures of the following compound (called guanidine) and state the hybridization of the four highlighted atoms. In which orbitals do the three lone pairs drawn reside?What is the hybridization state of the circled nitrogens? What kind of orbital contains the lone pairs identified in these circles? 1. sp, 2p 2. sp2, sp2 3. sp3, 2p 4. sp2, 2p The molecule shown on the right in the example in the right column is the amino acid histidine, and the five-membered ring is known as aromatic. An aromatic ring has 2, 6, 10, 14, etc., electrons placed in 2p orbitals around a ring. Indicate which of the following statements must therefore be true. 1. There are a total of six electrons in the pi system (defined as electrons in 2p orbitals), including the lone pair on the ring N that is not circled. 2. There are a total of six electrons in the pi system, including the lone pair on the ring N atom that is circled. 3. The lone pair on the ring N atom that is not circled resides in an sp2 orbital on an sp2 hybridized nitrogen atom. 4. Statements 2 and 3 are both true.CQ The following structure is called imidazolium. Which of the following statements about imidazolium are true? a. Both nitrogens are sp2 hybridized, and the lone pair of electrons is in a 2p orbital. b. The nitrogen on the right is sp3 hybridized, while the nitrogen on the left is sp2 hybridized. The lone pair of electrons is in an sp3 hybrid orbital. c. The molecule has an equivalent contributing structure not shown. d. The molecule has no reasonable contributing structures. 1. Statements a and c are true. 2. Statements a and d are true. 3. Statements b and c are true. 4. Statements b and d are true.Write the ground-state electron configuration for each atom. After each atom is its atomic number in parentheses. (a) Sodium (11) (b) Magnesium (12) (c) Oxygen (8) (d) Nitrogen (7)Identify the atom that has each ground-state electron configuration. (a) 1s2 2s2 2p6 3s2 3p4 (b) 1s2 2s2 2p4 Define valence shell and valence electron.How many electrons are in the valence shell of each atom? (a) Carbon (b) Nitrogen (c) Chlorine (d) Aluminum 1.24P 1.25P 1.26P Write Lewis structures for these compounds. Show all valence electrons. None of them contains a ring of atoms. (a) Hydrogen peroxide, H2O2 (b) Hydrazine, N2H4 (c) Methanol, CH3OH Write Lewis structures for these ions. Show all valence electrons and all formal charges. (a) Amide ion, NH2 (b) Bicarbonate ion, HCO3 (c) Carbonate ion, CO32 (d) Nitrate ion, NO3 (e) Formate ion, HCOO (f) Acetate ion, CH3COO 1.29P Some of these structural formulas are incorrect (i.e., they do not represent a real compound) because they have atoms with an incorrect number of bonds. Which structural formulas are incorrect? Which atoms in them have an incorrect number of bonds?Following the rule that each atom of carbon, oxygen, and nitrogen reacts to achieve a complete outer shell of eight valence electrons, add unshared pairs of electrons as necessary to complete the valence shell of each atom in these ions. Then assign formal charges as appropriate.Following are several Lewis structures showing all valence electrons. Assign formal charges in each structure as appropriate.Which statements are true about electronegativity? (a) Electronegativity increases from left to right in a period of the Periodic Table. (b) Electronegativity increases from top to bottom in a column of the Periodic Table. (c) Hydrogen, the element with the lowest atomic number, has the smallest electronegativity. (d) The higher the atomic number of an element, the greater its electronegativity.Why does fluorine, the element in the upper right comer of the Periodic Table, have the largest electronegativity of any element?Arrange the single covalent bonds within each set in order of increasing polarity. (a) CH, O H, NH (b) CH, BH, OH (c) CH, CCl, CI (d) CS, CO, CN (e) CLi, CB, CMg Using the values of electronegativity given in Table 1.5, predict which indicated bond in each set is more polar, and using the symbols + and , show the direction of its polarity. (a) CH3OH or CH3OH (b) CH3NH2 or CH3 PH2 (c) CH3 SH or CH3SH (d) CH3F or HF 1.37P Use VSEPR to predict bond angles about each highlighted atom.Use VSEPR to predict bond angles about each atom of carbon, nitrogen, and oxygen in these molecules.Use VSEPR to predict the geometry of these ions. (a) NH2 (b) NO2 (c) NO2+ (d) NO3 1.41P 1.42P What is the meaning of the term tertiary (3) when it is used to classify alcohols? Draw a structural formula for the one tertiary (3) alcohol with the molecular formula C4H10O.What is the meaning of the term tertiary (3) when it is used to classify amines? Draw a structural formula for the one tertiary (3) amine known as Hnigs base (N,N-diisopropylethylamine).Draw structural formulas for (a) The four primary (1) amines with the molecular formula C4H11N. (b) The three secondary (2) amines with the molecular formula C4H11N. (c) The one tertiary (3) amine with the molecular formula C4H11N.Draw structural formulas for the three tertiary (3) amines with the molecular formula C5H13N.1.47P Identify the functional groups in each compound.Draw a three-dimensional representation for each molecule. Indicate which ones have a dipole moment and in what direction it is pointing. (a) CH3F (b) CH2Cl2 (c) CH2ClBr (d) CFCl3 (e) CCl4 (f) CH2=CCl2 (g) CH2=CHCl (h) HCCCCH (i) CH3CN (j) (CH3)2C=O (k) BrCH=CHBr (two answers)Tetrafluoroethylene, C2F4, is the starting material for the synthesis of the polymer polytetrafluoroethylene (PTFE), one form of which is known as Teflon. Tetrafluoroethylene has a dipole moment of zero. Propose a structural formula for this molecule.Which statements are true about resonance contributing structures? (a) All contributing structures must have the same number of valence electrons. (b) All contributing structures must have the same arrangement of atoms. (c) All atoms in a contributing structure must have complete valence shells. (d) All bond angles in sets of contributing structures must be the same.1.52P 1.53P 1.54P Are the structures in each set valid contributing structures?State the orbital hybridization of each highlighted atom.Describe each highlighted bond in terms of the overlap of atomic orbitals.Following is a structural formula of the prescription drug famotidine, marketed by McNeil Consumer Pharmaceuticals Co. under the name Pepcid. The primary clinical use of Pepcid is for the treatment of active duodenal ulcers and benign gastric ulcers. Pepcid is a competitive inhibitor of histamine H2 receptors that reduces both gastric acid concentration and the volume of gastric secretions. (a) Complete the Lewis structure of famotidine showing all valence electrons and any formal positive or negative charges. (b) Describe each circled bond in terms of the overlap of atomic orbitals.Draw a Lewis structure for methyl isocyanate, CH3NCO, showing all valence electrons. Predict all bond angles in this molecule and the hybridization of each C, N, and O.What is the hybridization of the highlighted atoms in the following structures? What are your estimates for the bond angles around these highlighted atoms? In each case, in what kind of orbital does the lone pair of electrons on the nitrogen reside?Using cartoon representations, draw a molecular orbital mixing diagram for a CO bond. In your picture, consider the relative energies of C and O and how this changes the resulting bonding and antibonding molecular orbitals relative to a CC bond.In what kind of orbitals do the lone-pair electrons on the oxygen of acetone reside? Are they in the same plane as the methyl CH3 groups, or are they perpendicular to the methyl CH3 groups?Draw the delocalized molecular orbitals for the following molecule. Are both bonds of the triple bond involved in the delocalized orbitals?1.64AP Each compound contains both ions and covalent bonds. Draw the Lewis structure for each compound. Show with dashes which are covalent bonds and show with charges which are ions. (a) Sodium methoxide, CH3ONa (b) Ammonium chloride, NH4Cl (c) Sodium bicarbonate, NaHCO3 (d) Sodium borohydride, NaBH4 (e) Lithium aluminum hydride, LiAlH4 Predict whether the carbon-metal bond in these organometallic compounds is nonpolar covalent, polar covalent, or ionic. For each polar covalent bond, show the direction of its polarity using the symbols + and .1.67AP Phosphorus is immediately under nitrogen in the Periodic Table. Predict the molecular formula for phosphine, the compound formed by phosphorus and hydrogen. Predict the HPH bond angle in phosphine.Draw a Lewis structure for the azide ion, N3. (The order of atom attachment is NNN, and they do not form a ring.) How does the resonance model account for the fact that the lengths of the NN bonds in this ion are identical?Cyanic acid, HOCN, and isocyanic acid, HNCO, dissolve in water to yield the same anion on loss of H+. (a) Write a Lewis structure for cyanic acid. (b) Write a Lewis structure for isocyanic acid. (c) Account for the fact that each acid gives the same anion on loss of H+.In Chapter 6, we study a group of organic cations called carbocations. Following is the structure of one such carbocation, the tert-butyl cation. (a) How many electrons are in the valence shell of the carbon bearing the positive charge? (b) Using VSEPR, predict the bond angles about this carbon. (c) Given the bond angle you predicted in (b), what hybridization do you predict for this carbon?Many reactions involve a change in hybridization of one or more atoms in the starting material. In each reaction, identify the atoms in the organic starting material that change hybridization and indicate the change. We examine these reactions in more detail later in the course.Following is a structural formula of benzene, C6H6, which we study in Chapter 21. (a) Using VSEPR, predict each HCC and CCC bond angle in benzene. (b) State the hybridization of each carbon in benzene. (c) Predict the shape of a benzene molecule. (d) Draw important resonance contributing structures.Following are three contributing structures for diazomethane, CH2N2. This molecule is used to make methyl esters from carboxylic acids (Section 17.7C). (a) Using curved arrows, show how each contributing structure is converted to the one on its right. (b) Which contributing structure makes the largest contribution to the hybrid?(a) Draw a Lewis structure for the ozone molecule, O3. (The order of atom attachment is OOO, and they do not form a ring.) Chemists use ozone to cleave carbon-carbon double bonds (Section 6.5C). (b) Draw four contributing resonance structures; include formal charges. (c) How does the resonance model account for the fact that the length of each OO bond in ozone (128 pm) is shorter than the OO single bond in hydrogen peroxide (HOOH, 147 pm) but longer than the OO double bond in the oxygen molecule (123 pm)?The following two compounds are isomers; that is, they are different compounds with the same molecular formula. We discuss this type of isomerism in Chapter 5. (a) Why are these different molecules that do not interconvert? (b) Absorption of light by a double bond in a molecule excites one electron from a molecular orbital to a molecular orbital. Explain how this absorption can lead to interconversion of the two isomers.In future chapters, we will encounter carbanionsions in which a carbon atom has three bonds and a lone pair of electrons and bears a negative charge. Draw another contributing structure for the allyl anion. Now using cartoon representations, draw the three orbitals that represent the delocalized system (look at Figure 1.26 for a hint). Which of the three orbitals are populated with electrons?1.78AP Do the line-angle formulas in each pair represent the same compound or constitutional isomers?Draw line-angle formulas for the three constitutional isomers with the molecular formula C5H12.Write IUPAC names for these alkanes.Combine the proper prefix, infix, and suffix and write the IUPAC name for each compound.Write the molecular formula, IUPAC name, and common name for each cycloalkane.Write molecular formulas for each bicycloalkane, given its number of carbon atoms. (a) Hydrindane (9 carbons) (b) Decalin (10 carbons) (c) Norbornane (7 carbons)2.7P For 1,2-dichloroethane: (a) Draw Newman projections for all eclipsed conformations formed by rotation from 0 to 360 about the carbon-carbon single bond. (b) Which eclipsed conformation(s) has (have) the lowest energy? Which has (have) the highest energy? (c) Which, if any, of these eclipsed conformations are related by reflection?Following is a chair conformation of cyclohexane with the carbon atoms numbered 1 through 6. (a) Draw hydrogen atoms that are above the plane of the ring on carbons 1 and 2 and below the plane of the ring on carbon 4. (b) Which of these hydrogens are equatorial? Which are axial? (c) Draw the alternative chair conformation. Which hydrogens are equatorial? Which are axial? Which are above the plane of the ring? Which are below it?Draw the alternative chair conformation for the trisubstituted cyclohexane given in Example 2.10. Label all CH3/H 1,3-diaxial interactions in this chair conformation.Draw a chair conformation of 1,4-dimethylcyclohexane in which one methyl group is equatorial and the other is axial. Draw the alternative chair conformation and calculate the ratio of the two conformations at 25C.Which cycloalkanes show cis, trans isomerism? For each that does, draw both isomers.Following is a planar hexagon representation for one isomer of 1,2,4-trimethylcyclohexane. Draw the alternative chair conformations of this compound and state which of the two is more stable.Here is one cis,trans isomer of 3,5-dimethylcyclohexanol. Complete the alternative chair conformations.AQ BQ CQ Arrange the alkanes in each set in order of increasing boiling point. (a) 2-Methylbutane, 2,2-dimethylpropane, and pentane (b) 3,3-Dimethylheptane, 2,2,4-trimethylhexane, and nonane Write a line-angle formula for each condensed structural formula. (a) (b) (c) (CH3)2CHCH(CH3)2 (d) (e) (CH3)3CH (f) CH3(CH2)3CH(CH3)2 Write the molecular formula of each alkane.Using parentheses and subscripts, provide an even more abbreviated formula for each structural formula.Which statements are true about constitutional isomers? (a) They have the same molecular formula. (b) They have the same molecular weight. (c) They have the same order of attachment of atoms. (d) They have the same physical properties.2.20P Each member of the following set of compounds is an alcohol; that is, each contains an OH (hydroxyl group, Section 1.3A). Which line-angle formulas represent the same compound? Which represent constitutional isomers?Each of the following compounds is an amine (Section 1.3B). Which line-angle formulas represent the same compound? Which represent constitutional isomers?Each of the following compounds is either an aldehyde or a ketone (Section 1.3C). Which line-angle formulas represent the same compound? Which represent constitutional isomers?Draw structural formulas and write IUPAC names for the nine constitutional isomers with the molecular formula C7H16.Draw structural formulas for all of the following. (a) Alcohols with the molecular formula C4H10O (b) Aldehydes with the molecular formula C4H8O (c) Ketones with the molecular formula C5H10O (d) Carboxylic acids with the molecular formula C5H10O2 Write IUPAC names for these alkanes and cycloalkanes.Write structural formulas and line-angle formulas for the following alkanes and cycloalkanes. (a) 2,2,4-Trimethylhexane (b) 2,2-Dimethylpropane (c) 3-Ethyl-2,4,5-trimethyloctane (d) 5-Butyl-2,2-dimethylnonane (e) 4-(1-Methylethyl)octane (f) 3,3-Dimethylpentane (g) trans-1,3-Dimethylcyclopentane (h) cis-1,2-Diethylcyclobutane Explain why each is an incorrect IUPAC name and write the correct IUPAC name for the intended compound. (a) 1,3-Dimethylbutane (b) 4-Methylpentane (c) 2,2-Diethylbutane (d) 2-Ethyl-3-methylpentane (e) 2-Propylpentane (f) 2,2-Diethylheptane (g) 2,2-Dimethylcyclopropane (h) 1-Ethyl-5-methylcyclohexane For each IUPAC name, draw the corresponding structural formula and line-angle formula. (a) Ethanol (b) Butanal (c) Butanoic acid (d) Ethanoic acid (e) Heptanoic acid (f) Propanoic acid (g) Octanal (h) Cyclopentene (i) Cyclopentanol (j) Cyclopentanone (k) Cyclohexanol (l) Propanone Write the IUPAC name for each compound.2.31P Torsional strain resulting from eclipsed CH bonds is approximately 4.2 kJ (1.0 kcal)/mol, and that for eclipsed CH and CCH3 bonds is approximately 6.3 kJ (1.5 kcal)/mol. Given this information, sketch a graph of energy versus dihedral angle for propane.How many different staggered conformations are there for 2-methylpropane? How many different eclipsed conformations are there?Consider 1-bromopropane, CH3CH2CH2Br. (a) Draw a Newman projection for the conformation in which CH3 and Br are anti (dihedral angle 180). (b) Draw Newman projections for the conformations in which CH3 and Br are gauche (dihedral angles 60 and 300). (c) Which of these is the lowest energy conformation? (d) Which of these conformations, if any, are related by reflection?Consider 1-bromo-2-methylpropane and draw the following. (a) The staggered conformation(s) of lowest energy (b) The staggered conformation(s) of highest energy trans-1,4-Di-tert-butylcyclohexane exists in a normal chair conformation. cis-1,4-Di-tert-butylcyclohexane, however, adopts a twist-boat conformation. Draw both isomers and explain why the cis isomer is more stable in a twist-boat conformation.From studies of the dipole moment of 1,2-dichloroethane in the gas phase at room temperature (25C), it is estimated that the ratio of molecules in the anti conformation to gauche conformation is 7.6 to 1. Calculate the difference in Gibbs free energy between these two conformations.2.38P Following are the alternative chair conformations for trans-1,2-dimethylcyclohexane. (a) Estimate the difference in free energy between these two conformations. (b) Given your value in (a), calculate the percent of each chair present in an equilibrium mixture of the two at 25C.2.40P 2.41P Draw line-angle formulas for the cis and trans isomers of 1,2-dimethylcyclopropane.Name and draw structural formulas for all cycloalkanes with molecular formula C5H10. Include cis and trans isomers as well as constitutional isomers.Using a planar pentagon representation for the cyclopentane ring, draw structural formulas for the cis and trans isomers of the following. (a) 1,2-Dimethylcyclopentane (b) 1,3-Dimethylcyclopentane Gibbs free energy differences between axial-substituted and equatorial-substituted chair conformations of cyclohexane were given in Table 2.4. (a) Calculate the ratio of equatorial to axial tert-butylcyclohexane at 25C. (b) Explain why the conformational equilibria for methyl, ethyl, and isopropyl substituents are comparable but the conformational equilibrium for tert-butylcyclohexane lies considerably farther toward the equatorial conformation.2.46P Calculate the difference in Gibbs free energy in kilojoules per mole between the alternative chair conformations of: (a) trans-4-Methylcyclohexanol (b) cis-4-Methylcyclohexanol (c) trans-1,4-Dicyanocyclohexane Draw the alternative chair conformations for the cis and trans isomers of 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, and 1,4-dimethylcyclohexane. (a) Indicate by a label whether each methyl group is axial or equatorial. (b) For which isomer(s) are the alternative chair conformations of equal stability? (c) For which isomer(s) is one chair conformation more stable than the other?Use your answers from Problem 2.48 to complete the table showing correlations between cis,trans and axial,equatorial for disubstituted derivatives of cyclohexane. Draw the alternative chair conformations for the cis and trans isomers of 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane. (a) Indicate by a label whether each methyl group is axial or equatorial.There are four cis,trans isomers of 2-isopropyl-5-methylcyclohexanol: (a) Using a planar hexagon representation for the cyclohexane ring, draw structural formulas for the four cis,trans isomers. (b) Draw the more stable chair conformation for each of your answers in part (a). (c) Of the four cis,trans isomers, which is most stable? (Hint: If you answered this part correctly, you picked the isomer found in nature and given the name menthol.)Draw alternative chair conformations for each substituted cyclohexane and state which chair is more stable.1,2,3,4,5,6-Hexachlorocyclohexane shows cis,trans isomerism. At one time, a crude mixture of these isomers was sold as an insecticide. The insecticidal properties of the mixture arise from one isomer, known as lindane, which is cis-1,2,4,5-trans- 3, 6-hexachlorocyclohexane. (a) Draw a structural formula for 1,2,3,4,5,6-hexachlorocyclohexane disregarding, for the moment, the existence of cis,trans isomerism. What is the molecular formula of this compound? (b) Using a planar hexagon representation for the cyclohexane ring, draw a structural formula for lindane. (c) Draw a chair conformation for lindane and label which chlorine atoms are axial and which are equatorial. (d) Draw the alternative chair conformation of lindane and again label which chlorine atoms are axial and which are equatorial. (e) Which of the alternative chair conformations of lindane is more stable? Explain.2.53P What generalization can you make about the densities of alkanes relative to the density of water?What unbranched alkane has about the same boiling point as water? (Refer to Table 2.5 on the physical properties of alkanes.) Calculate the molecular weight of this alkane and compare it with that of water.Complete and balance the following combustion reactions. Assume that each hydrocarbon is converted completely to carbon dioxide and water. (a) Propane + O2 (b) Octane + O2 (c) Cyclohexane + O2 (d) 2-Methylpentane + O2 Following are heats of combustion per mole for methane, propane, and 2,2,4-trimeth-ylpentane. Each is a major source of energy. On a gram-for-gram basis, which of these hydrocarbons is the best source of heat energy?Following are structural formulas and heats of combustion of acetaldehyde and ethylene oxide. Which of these compounds is more stable? Explain.Without consulting tables, arrange these compounds in order of decreasing (less negative) heat of combustion: hexane, 2-methylpentane, and 2,2-dimethylbutane.Which would you predict to have the larger (more negative) heat of combustion, cis-1,4-dimethylcyclohexane or trans-1,4-dimethylcyclohexane?Following are structural formulas for 1,4-dioxane and piperidine. 1,4-Dioxane is a widely used solvent for organic compounds. Piperidine is found in small amounts in black pepper (Piper nigrum). (a) Complete the Lewis structure of each compound by showing all unshared electron pairs. (b) Predict bond angles about each carbon, oxygen, and nitrogen atom. (c) Describe the most stable conformation of each ring and compare these conformations with the chair conformation of cyclohexane.Following is a planar hexagon representation of L-fucose, a sugar component of the determinants of the A, B, O blood group typing. For more on this system of blood typing, see Chemical Connections: A, B, AB, and O Blood Group Substances in Chapter 25. (a) Draw the alternative chair conformations of L-fucose. (b) Which of them is more stable? Explain.On the left is a stereorepresentation of glucose (we discuss the structure and chemistry of glucose in Chapter 25). (a) Convert the stereorepresentation on the left to a planar hexagon representation. (b) Convert the stereorepresentation on the left to a chair conformation. Which substituent groups in the chair conformation are equatorial? Which are axial?2.64P 2.65P 3.1P Assign priorities to the groups in each set. (a) CH2OH and CH2CH2OH (b) CH2OH and CH=CH2 (c) CH2OH and C(CH3)3 3.3P Following are stereorepresentations for the four stereoisomers of 3-chloro-2-butanol. (a) Assign an R or S configuration to each chiral center. (b) Which compounds are enantiomers? (c) Which compounds are diastereomers?3.5P 3.6P How many stereoisomers exist for 1,3-cyclopentanediol?How many stereoisomers exist for 1,4-cyclohexanediol?3.9P 3.10P If the side chain of the amino add is a methyl group, the compound is referred to as alanine. What is the Cahn-Ingold-Prelog stereochemical descriptor for the chiral center in alanine? 1. It is a Z-stereocenter. 2. It is an S-stereocenter. 3. It is an E-stereocenter. 4. It is an R-stereocenter.BQ The amino acids cysteine and serine are shown. What are the Cahn-Ingold-Prelog stereochemical descriptors for these two amino acids? 1. Serine is S while cysteine is R. 2. Cysteine is S while serine is R. 3. Cysteine and serine are both R. 4. Cysteine and serine are both S.DQ As stated, proteins are stereochemically pure because only a single enantiomer of each amino acid building block is used by nature. How many stereoisomers are possible for a chain of only 3 chiral amino acids if both enantiomers of the amino acids are used? 1. 2 2. 4 3. 8 4. 16 As stated, proteins are stereochemically pure because only a single enantiomer of each amino acid building block is used by nature. How many stereoisomers are possible for a chain of only 3 chiral amino acids if both enantiomers of the amino adds are used? 1. 2 2. 4 3. 8 4. 16 3.11P One reason we can be sure that sp3-hybridized carbon atoms are tetrahedral is the number of stereoisomers that can exist for different organic compounds. (a) How many stereoisomers are possible for CHCl3, CH2Cl2, and CHClBrF if the four bonds to carbon have a tetrahedral arrangement? (b) How many stereoisomers would be possible for each of these compounds if the four bonds to the carbon had a square planar geometry?Which compounds contain chiral centers? (a) 2-Chloropentane (b) 3-Chloropentane (c) 3-Chloro-1-pentene (d) 1,2-Dichloropropane 3.15P 3.16P 3.17P Mark each chiral center in the following molecules with an asterisk. How many stereoisomers are possible for each molecule?3.19P Assign priorities to the groups in each set. (a) H CH3 OH CH2OH (b) CH2CH=CH2 CH=CH2 CH3 CH2COOH (c) CH3 H COONH3+ (d) CH3 CH2SH NH3+ CHO Following are structural formulas for the enantiomers of carvone. Each has a distinctive odor characteristic of the source from which it is isolated. Assign an R or S configuration to the single chiral center in each enantiomer. Why do they smell different when they are so similar in structure?Following is a staggered conformation for one of the enantiomers of 2-butanol. (a) Is this (R)-2-butanol or (S)-2-butanol? (b) Viewed along the bond between carbons 2 and 3, draw a Newman projection for this staggered conformation. (c) Draw a Newman projection for two more staggered conformations of this molecule. Which of your conformations is most stable? Assume that OH and CH3 are comparable in size.3.23P When oxaloacetic acid and acetyl-coenzyme A (acetyl-CoA) labeled with radioactive carbon-14 in position 2 are incubated with citrate synthase, an enzyme of the tricarboxylic acid cycle, only the following enantiomer of [2-l4C]citric acid is formed stereoselectively. Note that citric acid containing only 12C is achiral. Assign an R or S configuration to this enantiomer of [2-14C]citric acid. (Note: Carbon-14 has a higher priority than carbon-12.)3.25P Mark each chiral center in the following molecules with an asterisk. How many stereoisomers are possible for each molecule?3.27P 3.28P 3.29P 3.30P Which of the following are meso compounds?3.32P 3.33P Which of the following compounds are chiral? Which, if any, are meso? Which, if any, does not have a possible diastereomer?3.35P 3.36P 3.37P The chiral catalyst (R)-BINAP-Ru is used to hydrogenate alkenes to give alkanes (Section 6.7C). The products are produced with high enantiomeric excess. An example is the formation of (S)-naproxen, a pain reliever. (a) What kind of isomers are the enantiomers of BINAP? (b) How can one enantiomer of naproxen be formed in such high yield?3.39P For each conjugate acid-base pair, identify the first species as an acid or a base and the second species as its conjugate acid or conjugate base. In addition, draw Lewis structures for each species, showing all valence electrons and any formal charges. (a) H2SO4, HSO4 (b) NH3, NH2 (c) CH3OH, CH3O Write these reactions as proton-transfer reactions. Label which reactant is the acid and which is the base, which product is the conjugate base of the original acid, and which is the conjugate acid of the original base. In addition, write Lewis structures for each reactant and product and use curved arrows to show the flow of electrons in each reaction. (a) CH3SH+OHCH3S+H2O (b) CH2=O+HClCH2=OH++Cl Following is a structural formula for guanidine, the compound by which migratory birds excrete excess metabolic nitrogen. The hydrochloride salt of this compound is a white crystalline powder, freely soluble in water and ethanol. (a) Write a Lewis structure for guanidine showing all valence electrons. (b) Does proton transfer to guanidine occur preferentially to one of its NH2 groups (cation A) or to its NH group (cation B)? Explain.Write an equation to show the proton transfer between each alkene or cycloalkene and HCl. Where two carbocations are possible, show each.For each value of Ka, calculate the corresponding value of pKa. Which compound is the stronger acid? (a) Acetic add, Ka = 1.74 105 (b) Chloroacetic acid, Ka= 1.38 103 Predict the position of equilibrium and calculate the equilibrium constant, Keq, for each acid-base reaction. (a) (b)Calculate Keq for a reaction with G0 = 17.1 kJ/mol (4.09 kcal/mol) at 328 K. Compare this value to the 1 103 seen at 298 K.Acid-Base Equilibria Many factors contribute to the acidity of organic compounds. Electronegativity, resonance, induction, hybridization, aromaticity, and atomic size, all play a role. In the following comparisons, you are asked to identify the factor(s) that would be most important to analyze when predicting relative acidity, and then to predict the trend in acidity and pKa values. For each of the following pairs of compounds answer the following two multiple-choice questions. 1. What factor(s) are the most important to consider when predicting the relative acidity of the two compounds? a. Electronegativity of the atom possessing the hydrogen. b. Resonance stabilization of the anionic conjugate base. c. Inductive stabilization of the anionic conjugate base. d. Hybridization of the atom possessing the hydrogen. e. The atomic size of the atom possessing the hydrogen.What is the relative trend in acidity and pKa of the two compounds? a. Structure I is the most acidic, and Structure I has the highest pKa. b. Structure I is the most acidic, and Structure I has the lowest pKa. c. Structure II is the most acidic, and Structure I has the highest pKa. d. Structure II is the most acidic, and Structure I has the lowest pKa.Write an equation for the reaction between each Lewis acid-base pair, showing electron flow by means of curved arrows. (a) (CH3CH2)3B + OH (b) CH3Cl + AlCl3 For each conjugate acid-base pair, identify the first species as an acid or a base and the second species as its conjugate acid or base. In addition, draw Lewis structures for each species, showing all valence electrons and any formal charge. (a) HCOOH HCOO (b) NH4+ NH3 (c) CH3CH2O CH3CH2OH (d) HCO3 CO32 (e) H2PO4 HPO42 (f) CH3CH3 CH3CH2 (g) CH3S CH3SH Complete a net ionic equation for each proton-transfer reaction using curved arrows to show the flow of electron pairs in each reaction. In addition, write Lewis structures for all starting materials and products. Label the original acid and its conjugate base; label the original base and its conjugate acid. If you are uncertain about which substance in each equation is the proton donor, refer to Table 4.1 for the relative strengths of proton acids. (a) NH3+HCl (b) CH3CH2O+HCl (c) HCO3+OH (d) CH3COO+NH4+Arrange the compounds in each set in order of increasing base strength. Consult Table 4.1 for pKa values of the conjugate acid of each base.4.12P In acetic acid, CH3COOH, the OH hydrogen is more acidic than the CH3 hydrogens. Explain.Which has the larger numerical value? (a) The pKa of a strong acid or the pKa of a weak acid (b) The Ka of a strong acid or the Ka of a weak acid In each pair, select the stronger acid. (a) Pyruvic acid (pKa 2.49) or lactic acid (pKa 3.08) (b) Citric acid (pKa1 3.08) or phosphoric acid (pKa1 2.10)Arrange the compounds in each set in order of increasing acid strength. Consult Table 4.1 for pKa values of each acid.Arrange the compounds in each set in order of increasing base strength. Consult Table 4.1 for pKa values of the conjugate acid of each base.If the G for a reaction is 4.5 kcal/mol at 298 K, what is the Keq for this reaction? What is the change in entropy of this reaction if H = 3.2 kcal/mol?Calculate the Keq for the following reactions from the pKas given. State whether the reaction is exergonic or endergonic.4.20P Answer true or false to the following statements about the mechanism of acid-base reactions. (a) The acid and base must encounter each other by a collision in order for the proton to transfer. (b) All collisions between acids and bases result in proton transfer. (c) During an acid-base reaction the lone pair on the base fills the A-H antibonding sigma orbital.In each of the following three reaction coordinate diagrams, state: (a) Whether the reaction is exothermic or endothermic. (b) Whether the reaction is the slowest, the fastest, or intermediate in rate. (c) If all three reactions have the same entropy change between the reactant and product, which reaction has the largest favorable G0.The acid-base chemistry reaction of barium hydroxide (Ba(OH)2) with ammonium thiocyanate (NH4SCN) in water creates barium thiocyanate, ammonia, and water. The reaction is highly favorable, but is also so endothermic that the solutions cools to such an extent that a layer of frost forms on the reaction vessel. Explain how an endothermic reaction can be favorable.Unless under pressure, carbonic acid (H2CO3) in aqueous solution breaks down into carbon dioxide and water and carbon dioxide is evolved as bubbles of gas. Write an equation for the conversion of carbonic acid to carbon dioxide and water.4.25P Acetic acid, CH3COOH, is a weak organic acid, pKa 4.76. Write an equation for the equilibrium reaction of acetic acid with each base. Which equilibria lie considerably toward the left? Which lie considerably toward the right? (a) NaHCO3 (b) NH3 (c) H2O (d) NaOH Benzoic acid, C6H5COOH (pKa 4.19), is only slightly soluble in water, but its sodium salt, C6H5COO Na+, is quite soluble in water. In which solution(s) will benzoic acid dissolve? (a) Aqueous NaOH (b) Aqueous NaHCO3 (c) Aqueous Na2CO3 4.28P One way to determine the predominant species at equilibrium for an acid-base reaction is to say that the reaction arrow points to the acid with the higher value of pKa. For example, Explain why this rule works.Will acetylene react with sodium hydride according to the following equation to form a salt and hydrogen, H2? Using pKa values given in Table 4.1, calculate Keq for this equilibrium.4.31P For each equation, label the Lewis acid and the Lewis base. In addition, show all unshared pairs of electrons on the reacting atoms and use curved arrows to show the flow of electrons in each reaction. (a) F + BF3 BF4 Complete the equation for the reaction between each Lewis acid-base pair. In each equation, label which starting material is the Lewis acid and which is the Lewis base; use curved arrows to show the flow of electrons in each reaction. In doing this problem, it is essential that you show valence electrons for all atoms participating in each reaction. (a) (b) (c) (d)Each of these reactions can be written as a Lewis acid-Lewis base reaction. Label the Lewis acid and the Lewis base; use curved arrows to show the flow of electrons in each reaction. In doing this problem, it is essential that you show valence electrons for all atoms participating in each reaction.The sec-butyl cation can react as both a Brnsted-Lowry acid (a proton donor) and a Lewis acid (an electron pair acceptor) in the presence of a watersulfuric acid mixture. In each case, however, the product is different. The two reactions are as follows: (a) In which reaction(s) does this cation react as a Lewis acid? In which reaction(s) does it react as a Brnsted-Lowry acid? (b) Write Lewis structures for reactants and products and show by the use of curved arrows how each reaction occurs.4.36AP 4.37AP 4.38AP Explain why the hydronium ion, H3O+, is the strongest acid that can exist in aqueous solution. What is the strongest base that can exist in aqueous solution?What is the strongest base that can exist in liquid ammonia as a solvent?4.42AP 4.43AP Methyl isocyanate, CH3N=C=O, is used in the industrial synthesis of a type of pesticide and herbicide known as a carbamate. As a historical note, an industrial accident in Bhopal, India, in 1984 resulted in leakage of an unknown quantity of this chemical into the air. An estimated 200,000 people were exposed to its vapors, and over 2000 of these people died. (a) Write a Lewis structure for methyl isocyanate and predict its bond angles. What is the hybridization of its carbonyl carbon? Of its nitrogen atom? (b) Methyl isocyanate reacts with strong acids, such as sulfuric acid, to form a cation. Will this molecule undergo protonation more readily on its oxygen or nitrogen atom? In considering contributing structures to each hybrid, do not consider structures in which more than one atom has an incomplete octet.Offer an explanation for the following observations. (a) H3O+ is a stronger acid than NH4+. (b) Nitric acid, HNO3, is a stronger acid than nitrous acid, HNO2. (c) Ethanol and water have approximately the same acidity. (d) Trifluoroacetic acid, CF3COOH, is a stronger acid than trichloroacetic acid, CCl3COOH.4.46AP Alcohols (Chapter 10) are weak organic acids, pKa 1518. The pKa of ethanol, CH3CH2OH, is 15.9. Write equations for the equilibrium reactions of ethanol with each base. Which equilibria lie considerably toward the right? Which lie considerably toward the left? (a) NaHCO3 (b) NaOH (c) NaNH2 (d) NH3 As we shall see in Chapter 19, hydrogens on a carbon adjacent to a carbonyl group are far more acidic than those not adjacent to a carbonyl group. The anion derived from acetone, for example, is more stable than is the anion derived from ethane. Account for the greater stability of the anion from acetone.2,4-Pentanedione is a considerably stronger acid than is acetone (Chapter 19). Write a structural formula for the conjugate base of each acid and account for the greater stability of the conjugate base from 2,4-pentanedione.Write an equation for the acid-base reaction between 2,4-pentanedione and sodium ethoxide and calculate its equilibrium constant, Keq. The pKa of 2,4-pentanedione is 9; that of ethanol is 15.9.4.51AP 4.52AP 4.53AP Following is a structural formula for imidazole, a building block of the essential amino acid histidine (Chapter 27). It is also a building block of histamine, a compound all too familiar to people with allergies and takers of antihistamines. When imidazole is dissolved in water, proton transfer to it gives a cation. Is this cation better represented by structure A or B? Explain.Calculate the index of hydrogen deficiency for 1-hexene, C6H10, and account for this deficiency by reference to its structural formula.5.2P Write the IUPAC name of each alkene. (a) (b)5.4P 5.5P 5.6P 5.7P 5.8P Predict all approximate bond angles about each highlighted carbon atom. To make these predictions, use valence-shell electron-pair repulsion (VSEPR) theory (Section 1.4). (a) (b) (c) (d) (e)5.10P The structure of 1,2-propadiene (allene) is shown to the right. (a) Predict all approximate bond angles in this molecule. (b) State the orbital hybridization of each carbon. (c) Explain the three-dimensional geometry of allene in terms of the orbitals used.5.12P Draw structural formulas for these alkenes. (a) trans-2-Methyl-3-hexene (b) 2-Methyl-2-hexene (c) 2-Methyl-1-butene (d) 3-Ethyl-3-methyl-1-pentene (e) 2,3-Dimethyl-2-butene (f) cis-2-Pentene (g) (Z)-1-Chloropropene (h) 3-Methylcyclohexene (i) 1-Isopropyl-4-methylcyclohexene (j) (E)-2,6-Dimethyl-2,6-octadiene (k) 3-Cyclopropyl-1-propene (l) Cyclopropylethene (m) 2-Chloropropene (n) Tetrachloroethylene (o) 1-Chlorocyclohexene Name these alkenes and cycloalkenes.5.15P 5.16P 5.17P For each molecule that shows cis, trans isomerism, draw the cis isomer.-Ocimene, a triene found in the fragrance of cotton blossoms and several essential oils, has the IUPAC name (Z)-3,7-dimethyl-1,3,6-octatriene. Draw a structural formula for -ocimene.5.20P 5.21P 5.22P 5.23P 5.24P Measure the CH3,CH3 distance in the energy-minimized model of cis-2-butene and the CH3,H distance in the energy-minimized model of trans-2-butene. In which isomer is the nonbonded interaction strain greater?5.26P Measure the CCC and CCH bond angles in the energy-minimized model of cyclohexene and compare them with those predicted by VSEPR. Explain any differences.5.28P 5.29P 5.30P 5.31P 5.32P 5.33P Pyrethrin II and pyrethrosin are two natural products isolated from plants of the chrysanthemum family. Pyrethrin II is a natural insecticide and is marketed as such. (a) Label all chiral centers in each molecule and all carbon-carbon double bonds about which there is the possibility for cis,trans isomerism. (b) State the number of stereoisomers possible for each molecule. (c) Show that the bicyclic ring system of pyrethrosin is composed of three isoprene units. (d) Calculate the index of hydrogen deficiency for each of these natural products.5.35P 5.36P Bromine adds to cis- and trans-2-butene to give different diastereomers of 2,3-dibromobutane. What does this say about the mode of addition of bromine to this alkene? We discuss the addition of bromine to alkenes in Chapter 6.Using the BDE values from Appendix 3, calculate the Hrxn0 value and state if the reaction below is exothermic or endothermic. CH2=CH2 + HCl CH3CH2Cl Name and draw a structural formula for the product of each alkene addition reaction. (a) (b)6.3P Propose a mechanism for the addition of HI to 1-methylcyclohexene to give 1-iodo-1-methylcyclohexane. Which step in your mechanism is rate-determining?6.5P Propose a mechanism for the acid-catalyzed hydration of 1-methylcyclohexene to give 1-methylcyclohexanol. Which step in your mechanism is rate-determining?The acid-catalyzed hydration of 3,3-dimethyl-1-butene gives 2,3-dimethyl- 2-butanol as the major product. Propose a mechanism for the formation of this alcohol.Complete these reactions. (a) (b)Draw the structure of the chlorohydrin formed by treating 1-methylcyclohexene with Cl2/H2O.Draw structural formulas for the alkene that gives each alcohol upon hydroboration-oxidation. (a) (b)6.11P

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