Chapter 7, ULTRAVIOLET SPECTROSCOPY Video Solutions, Introduction to Spectroscopy

Problem 1

The ultraviolet spectrum of benzonitrile shows a primary absorption band at $224 \mathrm{~nm}$ and a secondary band at $271 \mathrm{~nm}$.
(a) If a solution of benzonitrile in water, with a concentration of $1 \times 10^{-4}$ molar, is examined at a wavelength of $224 \mathrm{~nm}$, the absorbance is determined to be 1.30 . The cell length is $1 \mathrm{~cm}$. What is the molar absorptivity of this absorption band?
(b) If the same solution is examined at $271 \mathrm{~nm}$, what will be the absorbance reading $(\varepsilon=1000)$ ? What will be the intensity ratio, $I_0 / I$ ?

Benjamin Smith

Numerade Educator

07:27

Problem 2

Draw structural formulas that are consistent with the following observations:
(a) An acid $\mathrm{C}_7 \mathrm{H}_4 \mathrm{O}_2 \mathrm{Cl}_2$ shows a UV maximum at $242 \mathrm{~nm}$.
(b) A ketone $\mathrm{C}_8 \mathrm{H}_{14} \mathrm{O}$ shows a UV maximum at $248 \mathrm{~nm}$.
(c) An aldehyde $\mathrm{C}_8 \mathrm{H}_{12} \mathrm{O}$ absorbs in the $\mathrm{UV}$ with $\lambda_{\max }=244 \mathrm{~nm}$.

Zubair Abdulla

Numerade Educator

02:07

Problem 3

Predict the UV maximum for each of the following substances:
DIAGRAM CANT COPY

Lottie Adams

Numerade Educator

02:26

Problem 4

The UV spectrum of acetone shows absorption maxima at 166,189 , and $279 \mathrm{~nm}$. What type of transition is responsible for each of these bands?

Prashant Bana

Numerade Educator

02:04

Problem 5

Chloromethane has an absorption maximum at $172 \mathrm{~nm}$, bromomethane shows an absorption at $204 \mathrm{~nm}$, and iodomethane shows a band at $258 \mathrm{~nm}$. What type of transition is responsible for each band? How can the trend of absorptions be explained?

Crystal Wang

Numerade Educator

03:23

Problem 6

What types of electronic transitions are possible for each of the following compounds?
(a) Cyclopentene
(b) Acetaldehyde
(c) Dimethyl ether
(d) Methyl vinyl ether
(e) Triethylamine
(f) Cyclohexane

Tianyu Li

Numerade Educator

02:31

Problem 7

Predict and explain whether UV/visible spectroscopy can be used to distinguish between the following pairs of compounds. If possible, support your answers with calculations.
DIAGRAM CANT COPY

George Bennett

Numerade Educator

06:30

Problem 8

(a) Predict the UV maximum for the reactant and product of the following photochemical reaction:
DIAGRAM CANT COPY
(b) Is UV spectroscopy a good way to distinguish the reactant from the product?
(c) How would you use infrared spectroscopy to distinguish between the reactant and the product?
(d) How would you use proton NMR to distinguish between the reactant and the product (two ways)?
(e) How could you distinguish between the reactant and the product by using DEPT NMR (see Chapter 10)?

Madeline Currie

Numerade Educator