Organic Chemistry - Standalone book
10th Edition
ISBN: 9780073511214
Author: Francis A Carey Dr., Robert M. Giuliano
Publisher: McGraw-Hill Education
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Chapter 7.14, Problem 22P
Write structural formulas for all the
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Question 3
Some photophysical parameters (lifetime, t, and quantum yield, $) for fluorescence (n = 370 nm)
and phosphorence (p = 580 nm) of pyrene, 1-chloropyrene and 1-bromopyrene are given in the
table below, as measured at room temperature (RT) and at 77 K in a frozen ethanol glass.
фе
τη
Фл
Фр
Tp
(RT)
(RT)
(77 K)
(77 K)
(77 K)
(ns)
(s)
X = H
0.72
530
0.9
< 0.001
0.39
X
X = CI
0.22
75
0.59
0.058
0.10
X = Br 0.032 2
0.17
0.085
0.004
fl = fluorescence; p = phosphorescence
(a) Construct a Jablonski diagram for pyrene (X = H) at 77K.
(b) Pyrene (X = H) has an absorbance maximum, Amax, at 330 nm and a fluorescence
maximum, 11, at 370 nm. Why does this difference in wavelengths occur?
(c) Explain why the lifetime for phosphorescence is longer than that for fluorescence.
(d) Why does the fluorescence quantum yield increase with decreasing temperature?
(e) Explain the trend in phosphorescence quantum yield as X is varied.
Question 4
The photoisomerization of alkenes is a photochemical transformation between the E- and
Z-stereoisomers. The irradiation of the E-isomer (shown below) with radiation at 340 nm gives an
E:Z ratio of 5:95. Some relevant information for each compound is shown in the table below.
Amax
340nm
E290
E340
(L mol¹ cm¹) (L mol¹ cm-1)
E
340 nm
8000
20000
PE-Z = 0.60
Z
290 nm 16000
2000
Oz-E = 0.30
(a) The reaction proceeds through an excited state. Explain the nature of this excited state, and
explain how it allows formation of the E- and Z-isomers. Explain why this isomerisation is
unlikely to occur thermally.
(b) The product of the equilibrium shown above gives a final ratio with substantially more of one
isomer. Explain why this occurs.
(c) Explain why the starting concentration of isomers does not affect the final ratio after
irradiation.
(d) If the irradiating wavelength used was changed to 290 nm and you started with Z- rather
than E-isomer, use the data in the table above to…
Question 5
The photoisomerisation of cinnamonitriles (shown below) has been used as a model for the
molecular transformations that lead to vision in mammals. The outcome of the reaction under
various conditions is shown in the table below.
CN
sensitizer
visible light
忌
CN
СОН
HO..
OH
OH
N
NH
'N'
Riboflavin
Starting isomer
E
Sensitizer
Riboflavin
Radiation
No light
Final Z:E ratio
0:100
E
No sensitizer
402 nm
4:96
E
Riboflavin
402 nm
99:1
Z
Riboflavin
402 nm
99:1
(a) Explain what is happening in the photoisomerisation reaction above.
(b) Give the structure of the intermediate that allows the reaction to occur, and explain how it
forms.
(c) Explain why each reaction gives the particular E:Z ratio that it does, and why it is considered
photostationary.
(d) Explain the role of the sensitizer, riboflavin, and why it is a requirement for this reaction.
(e) Explain why the irradiation of both the E- and Z-isomers in the presence of riboflavin gives the
same result. What would be the final…
Chapter 7 Solutions
Organic Chemistry - Standalone book
Ch. 7.1 - Name each of the following using IUPAC...Ch. 7.1 - Prob. 2PCh. 7.2 - How many carbon atoms are sp2-hybridized in the...Ch. 7.3 - Prob. 4PCh. 7.3 - Are cis-2-hexene and trans-3-hexene stereoisomers?...Ch. 7.4 - Prob. 6PCh. 7.4 - Prob. 7PCh. 7.4 - Give the IUPAC name of each of the compounds in...Ch. 7.5 - Arrange the following in order of increasing...Ch. 7.6 - Prob. 10P
Ch. 7.6 - Standard enthalpies of formation are known for all...Ch. 7.6 - Prob. 12PCh. 7.6 - Despite numerous attempts, the alkene...Ch. 7.6 - Write structural formulas for the six isomeric...Ch. 7.7 - Place a double bond in the carbon skeleton shown...Ch. 7.9 - Identify the alkene obtained on dehydration of...Ch. 7.10 - Prob. 17PCh. 7.11 - Prob. 18PCh. 7.12 - Prob. 19PCh. 7.13 - The alkene mixture obtained on dehydration of...Ch. 7.14 - Write the structures of all the alkenes that can...Ch. 7.14 - Write structural formulas for all the alkenes that...Ch. 7.15 - A study of the hydrolysis behavior of...Ch. 7.15 - Use curved arrows to illustrate the electron flow...Ch. 7.15 - Predict the major product of the reaction shown.Ch. 7.16 - Prob. 26PCh. 7.17 - Prob. 27PCh. 7.18 - Prob. 28PCh. 7.19 - Predict the major organic product of each of the...Ch. 7.19 - A standard method for the synthesis of ethers is...Ch. 7 - Write structural formulas for each of the...Ch. 7 - Prob. 32PCh. 7 - Give an IUPAC name for each of the following...Ch. 7 - A hydrocarbon isolated from fish oil and from...Ch. 7 - Prob. 35PCh. 7 - Prob. 36PCh. 7 - Prob. 37PCh. 7 - Prob. 38PCh. 7 - Choose the more stable alkene in each of the...Ch. 7 - Suggest an explanation for the fact that...Ch. 7 - Prob. 41PCh. 7 - Write structural formulas for all the alkene...Ch. 7 - Prob. 43PCh. 7 - Prob. 44PCh. 7 - Predict the major organic product of each of the...Ch. 7 - Prob. 46PCh. 7 - Prob. 47PCh. 7 - The rate of the reaction In the first order in...Ch. 7 - Prob. 49PCh. 7 - Prob. 50PCh. 7 - You have available 2,2-dimethylcyclopentanol (A)...Ch. 7 - Prob. 52PCh. 7 - Prob. 53PCh. 7 - Prob. 54PCh. 7 - Acid-catalyzed dehydration of...Ch. 7 - The ratio of elimination to substitution is...Ch. 7 - Prob. 57PCh. 7 - Prob. 58DSPCh. 7 - Prob. 59DSPCh. 7 - Prob. 60DSPCh. 7 - Prob. 61DSPCh. 7 - A Mechanistic Preview of Addition Reactions The...Ch. 7 - Prob. 63DSPCh. 7 - Prob. 64DSPCh. 7 - Prob. 65DSP
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- Can someone explain this to me?arrow_forwardCan someone explain this to me?arrow_forwardQuestion 4 The complex shown below, [Ru(bpy)2L]2+ (in which R = H in L), has a pendant anthracene group, and emits light at the same wavelength as [Ru(bpy)3]2+, but with a substantially longer lifetime and a higher quantum yield, as shown in the table below. Ru R Amax (nm) Aem (nm) (us) Ru(bpy)3²+ 440 616 0.75 0.045 Ru(bpy)2L2+ 440 614 51 0.19 (a) Draw a Jablonski diagram for the [Ru(bpy)2L]²* complex and use it to explain why the emission occurs at the same wavelength while the lifetime increases. (b) Explain why the quantum yield increases when the pendant anthracene is included. (c) At 77 K, [Ru(bpy)2L]²* emits light at = 400 nm, while anthracene emits at 397 nm. Explain why the emission wavelength changes. (d) What do you predict would occur to the emission characteristics (maximum, lifetime, and quantum yield) if the anthracene group was substituted with a bromine atom (i.e., R = Br).arrow_forward
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