The addition of OH radical to β-carotene is slightly less thermodynamically favourable than the H-atom abstraction reactions. The free energy of the OH-radical addition reactions to the 15E and 15Z isomers is illustrated in Figure 5 and the thermochemistry of the reactions calculated at various levels are summarized in Table 4. The OH radical addition reactions are more entropy driven in the solvent medium than in the gas phase. The OH-radical adduct resulting from the 15Z isomer is more exergonic by ~ 15 kJ/mol than the OH-radical adduct at the 15E isomer in all the three phases studied. A previous study on the addition of NO2 radical to C5-position of β-carotene reported the reaction to be endergonic in the polar and non-polar solvents.13 The exergonicity of the OH-radical additions to β-carotene is attributed to the high reactivity of OH radical compared to that of NO2 radical. On comparing with the H-atom abstraction reactions, the OH radical addition reactions are less entropy driven owing to the fact that the addition reactions can occur spontaneously only at low temperatures. Similar to the H-atom abstraction reactions, the addition reaction to 15Z isomer is equally favourable as that of the all-trans isomer. It is interesting …show more content…
The addition of the OH radical to the C5-position of β-carotene has an effect on the orientation of the β-ionone rings on both the isomers. Further, the conjugated system along the polyene chain is modified, as evident from the C-C single and double bond distances shown in Figure 5. In both the isomers, the conformation of the hydroxyl group pointing away from the methyl group is found to be energetically more stable. The spin is delocalized over the polyene chain and also in the -CH2 groups. This result in a larger degree of conjugation in the central part of the polyene chain and also the spin in the central part of the chain remains no
Decomposition and Synthesis Introduction: The purpose of the lab is to investigate what happens to the elements and compounds involved in the decomposition and synthesis reaction after their reaction. In a decomposition reaction, a compound is broken down into its component elements. For example, the electrolysis of water into oxygen and hydrogen gas:2 H2O → 2 H2 + O2(Helmenstine, 2016) In a synthesis reaction, two or more chemical species combine into a more complex compound.
The purpose of this experiment is to distinguish the relationships between reactants and products, in addition to expanding on concepts such as single displacement reactions, mole ratio values, moles to mass, theoretical yields, limiting reactants, excess, stoichiometric relationships and percentage errors.
Reaction 3 favors SN1. Since the solvent is polar protic, there is a weak nucleophile, and there is a secondary substituent. For this reaction there were two products, the minor being 3-chloro-2,4-dimethylpentane and the major being 2-chloro-2,4-dimethylpentane. Chemical reactions help scientists organize and understand how substances transform periods.
CHE341Homework Assignment #10Due:Monday16Novemberat6:00PM1.Aunimoleculargas-phasereactionX→Yis activated with collisions by an unreactivecollision partner Bwith the following mechanism:X+Bk1k−1⎯→⎯⎯←⎯⎯⎯X*+B,X*k2⎯→⎯Y,has a rate that follows the effective rate equationdY[]dt=kuniX[]. (a) Apply the steady state approximation (SSA) to determine an algebraicexpression forkuniin terms terms of the rate constantsk1,k–1andk2as well as [B]. (b)Discusshow the rate law changes in the limit of large and small [B].2.Dissociation of ethane into methyl radicalsfollowsfirst-order kinetics with ArrheniusparametersA=2.50×1016s–1andEa=367.6kJ mol–1. Calculate the Gibbs energy ofactivation, the entropy of activation and the enthalpy of activation at500 K.3.
The purpose of this lab was to experimentally and scientifically ascertain the percentage of oxygen in Chem B at Woonsocket High School. It was hypothesized that if the percentage of oxygen is measured experimentally in Chem B at Woonsocket High School, then it would be higher than the percentage of oxygen in dry air, which is 20.95%, because the air is not dry due to moisture in the air from people breathing and the altitude of where the experiment takes place may affect it as well.
Radicals are further formed in the propagation step, and are combined during the termination step. Since any of the radicals can combine in the termination step, a radical-initiated reaction can produce a mixture of products.3 The purpose of this experiment is to obtain a mixture of isomeric dichlorobutane in order to discover the relative reactivities of 1-chlorobutane through radical initiated chlorination. Instead of heat or light, the initiator used in the experiment is 2,2’-azobis-(2-methylpropionitrile).4 Identification of the products obtained in the experiment was done through the analysis of data from mass spectrometry, gas chromatography, and physical properties (e.g. boiling point and molecular weight).
As for the reaction itself, the formation of the radical follows the 3 step process of Initiation, Propagation, and Termination. The short run down of this is that the initiation step makes the radical via hydrogen abstraction, the propagation step forms products, and the termination ends the reaction and gives stable products. The rate determining step in this reaction is in the hydrogen abstraction. During hydrogen
Timberlake, K. C. (01/2014). Chemistry: An Introduction to General, Organic, and Biological Chemistry, 12th Edition.
Determining how a mechanism comes to be is crucial as a scientist and arriving to conclusions is a crucial component which lead to examining and determining which mechanism takes place when two or more substrates are made to react. At the end of the experiment a mechanism was determined based on the purified product’s melting point. This was accomplished by having the reaction take place but also through acquiring the melting point and comparing the number to the melting point which was already established by the scientific community. (Q1) When 0.252 g of trans-cinnamic acid was mixed in 2.5 mL glacial acetic acid and 0.434g pyridinium tribromide was added, the resulting product reflects an addition reaction. In general, reactions take place to achieve its lowest Gibb’s free energy because it’s at
In this preparative lab, an aldol (trans-p-anisalacetophenone) was produced from the reaction between p-anisaldehyde and acetophenone with the presence sodium hydroxide. The reaction also showed the importance of an enolate and the role it played in the mechanism. Sodium hydroxide acts as a catalyst in this experiment and is chosen because of its basic conditions and pH. The acetophenone carries an alpha hydrogen that has a pKa between 18 and 20. This alpha hydrogen is acidic because of its location near the carbonyl on acetophenone. When the sodium hydroxide is added, it deprotonates the hydrogen and creates an enolate ion. This deprotonation creates a nucleophilic carbon that can attack an electrophilic carbon (like a parent
The main objective is not only to reach the optimum ratio to generate the greatest amount of heat and temperature, but also to maintain a constant volume throughout the entire experiment.
The carbon-carbon double bond of alkenes represents a site that has a high electron intensity. This site is susceptible to oxidation. Depending on the conditions or reagents used to initiate the oxidation of alkenes, various products can be obtained. With relative mild oxidation, it is only the pi bond of an alkene that is cleaved resulting in the production of 1,2-diols or epoxides. However, when there is more vigorous
Introduction: The theory behind this experiment is the heat of a reaction (∆E) plus the work (W) done by a reaction is equal to
The polyene chain present in carotenoids is a highly reactive, electron rich system that is susceptible to attack by electrophilic reagents. In nature, carotenoids exist in the all-trans configuration, and they can isomerize to cis configuration under the influence of heat, light or certain chemical reactions e.g. quenching of the singlet oxygen species (Schieber & Carle 2005; Stahl & Sies 1996). The isomeric forms of lycopene common in foods are 5-cis, 9-cis, 13-cis and 15-cis with stability sequence being 5-cis, > all-trans >9-cis > 13-cis >15-cis in organic solvents (Singh & Goyal 2008; Lambelet et al. 2009). For β-carotene, its common isomeric forms are 9-cis, 13-cis, and 15-cis. In general, the cis- configuration can be incorporated better
This paper is about chemical reactions and chemical reaction types. All the data gathered was from conducting multiple experiments. Each experiment was performed carefully and analyzed to obtain the necessary information for the paper. That information included the four signs of a chemical change, the rnx type, and more.