Deck 12: Spectroscopy and Structure Determination

Question 1

Bending vibrations in the infared region occur at:

A) 3000 cm^-1
B) 2200 cm^-1
C) 1700 cm^-1
D) below 1400 cm^-1
E) over 3000 cm^-1

Answer 1

below 1400 cm^-1

Question 2

The area in the infared spectrum between 1400 and 400 cm^-1 is called the .

A) solid region
B) fingerprint region
C) functional group region
D) location region
E) none of these

Answer 2

fingerprint region

Question 3

Which bond would show a sharp absorption in the IR between 3000 and 2800 cm^-1?

A) O-H
B) N-H
C) C=O
D) C-H
E) C-O

Answer 3

C-H

Question 4

An IR spectrum of an unknown organic molecule having the formula C₃H₆O₂ reveals strong absorptions at 2500-3400 cm^-1, 1715 cm^-1, and 1230 cm^-1.To what class of compounds does the unknown belong?

A) alcohol
B) carboxylic acid
C) aldehyde
D) ester
E) ether

Question 5

As the wavelength of the radiation increases, the _______ decreases.

A) energy
B) frequency
C) wave number
D) all of these
E) all increase

Question 6

An IR spectrum of an unknown organic molecule having the molecular formula of C₄H₈O shows no absorptions at 1630-1780 cm^-1 or at 3200-3500 cm^-1.To what class of compounds does the unknown belong?

A) alcohol
B) carboxylic acid
C) ketone
D) ether
E) aldehyde

Question 7

How many peak(s) would you expect to see in the ¹H NMR spectrum of 1-bromobutane?

A) 1
B) 2
C) 3
D) 4
E) more than 4

Question 8

As the wavelength of the radiation decreases, the increases.

A) energy
B) frequency
C) wave number
D) all of these
E) all decrease

Question 9

An IR spectrum of an unknown organic molecule having the formula C₃H₆O reveals a strong absorption at 1230 cm^-1 and has no absorption over 3000 cm^-1.To what class of compounds does the unknown belong?

A) alcohol
B) amine
C) aldehyde
D) alkyne
E) ether

Question 10

Which of the following forms of electromagnetic radiation has the highest energy?

A) radiowaves
B) infrared
C) visible
D) uv
E) x-ray

Question 11

Which of the following compounds will not have a broad band in the 3000 to 3600 cm^-1 region of its IR spectrum?

A)
B)
C)
D)
E)

Question 12

How many peaks would you expect to see in the ¹H NMR spectrum for the following compound:

A) 1
B) 2
C) 3
D) 4
E) more than 4

Question 13

Which bond would show a strong, broad absorption in the IR between 3600 and 3200 cm^-1?

A) O-H
B) C-Cl
C) C=O
D) C-H
E) C-O

Question 14

Which of the following forms of electromagnetic radiation has the longest wavelength?

A) radiowaves
B) infrared
C) visible
D) uv
E) x-ray

Question 15

Which bond would show a strong, sharp absorption in the IR between 1200 and 1000 cm^-1?

A) O-H
B) N-H
C) C=O
D) C-H
E) C-O

Question 16

Which bond would show a strong, sharp absorption in the IR between 1800 and 1700 cm^-1?

A) O-H
B) N-H
C) C=O
D) C-H
E) C-O

Question 17

An IR spectrum of an unknown organic molecule having the formula C₃H₆O reveals a strong absorption at 1725 cm^-1.To what class of compounds does the unknown belong?

A) acid chloride
B) alkene
C) ketone
D) alkyne
E) phenol

Question 18

An IR spectrum of an unknown organic molecule having the formula C₂H₄O reveals a strong absorption at 1715-1725 cm^-1.To what class of compounds does the unknown belong?

A) alcohol
B) amine
C) aldehyde
D) alkyne
E) ether

Question 19

In the ¹H NMR spectrum of the following molecule, the protons on which carbon will have the most downfield chemical shift?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 20

The IR spectrum stretching frequency that has the highest energy occurs for which of these bonds?

A) O-H
B) C-O
C) C-Cl
D) C-H
E) C-C

Question 21

Which molecule will produce two lines in the proton decoupled ¹³C NMR spectrum?

A) CH₃CH₂OH
B) CH₃OCH₃
C) CH₃CH₂CH₂OH
D) CH₃OCH₂CH₃
E)

Question 22

Which of the following compounds is most likely to absorb ultraviolet radiation in the range of 200 to 400 nm?

A)
B)
C)
D)
E)

Question 23

Which of the following molecules has more than three (3) different types of protons in its ¹H NMR?

A) I
B) II
C) III
D) IV
E) V

Question 24

The compound will show what number of peaks in its ¹H decoupled ¹³C NMR spectrum?

A) 3
B) 4
C) 5
D) 6
E) 9

Question 25

A compound with the molecular formula C₅H₁₂ gave the following ¹H NMR spectrum: singlet, $\delta$ 1.0 (12 H)
The structure of this compound is:

A) I
B) II
C) III
D) IV
E) all are possible

Question 26

Which of the following molecules will show two peaks with an area ratio of 6:4 in its ¹H NMR spectrum?

A) I
B) II
C) III
D) IV
E) V

Question 27

Which of following will have three peaks in its ¹H decoupled ¹³C NMR spectrum?

A) pentane
B) isopentane
C) isobutane
D) benzene
E) m-chlorotoluene

Question 28

The following compound will have an ¹H NMR spectrum that consists of:

A) two singlets, area ratio 6:4.
B) three singlets, area ratio 3:3:4.
C) four singlets, area ratio 3:3:2:2.
D) two singlets and two doublets, area ratio 3:3:2:2.
E) two triplets and a singlet, area ratio 3:3:4.

Question 29

The following compound will have a proton NMR spectrum that shows:

A) two singlets, area ratio 3:1.
B) two singlets, area ratio 9:1.
C) three singlets, area ratio 3:3:6.
D) four singlets, area ratio 3:2:6:1.
E) six singlets, area ratio 3:3:3:1:1:1.

Question 30

How many peaks would you expect in the proton decoupled ¹³C NMR spectrum of 3-bromopentane?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 31

Which of the following molecules would absorb at the longest wavelength in the ultraviolet region?

A) hexane
B) 2-hexene
C) 2,4-hexadiene
D) 1,3,5-hexatriene
E) cyclohexane

Question 32

A compound C₃H₃Cl₅ has a ¹H NMR spectrum that consists of a triplet at $\delta$ 4.5 and a doublet at $\delta$ 6.0 (J = 7 Hz) with relative areas 1:2.Its structure is

A) CH₃CCl₂CCl₃
B) CH₂ClCCl₂CHCl₂
C) CHCl₂CCl₂CCH₂Cl
D) CHCl₂CHClCHCl₂
E) CH₂ClCHClCCl₃

Question 33

A monochloroalkane shows two parent ion peaks m/z at 92 and 94.What is the molecular formula?

A) C₄H₉Cl
B) C₃H₇Cl
C) C₃H₂₁Cl
D) C₄H₇Cl
E) C₂H₆Cl

Question 34

Compounds that will show only two sharp singlets in their ¹H NMR spectra are:

A) 1 and 2
B) 3
C) 1 and 3
D) 1 and 4
E) 1, 2, and 4

Question 35

The proton(s) on which C will produce a splitting pattern that is a doublet in its ¹H NMR spectrum?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 36

The following compounds in order of increasing wavelength of maximum UV-VIS absorption are

A) 1 < 2 < 3 < 4
B) 1 < 4 < 2 < 3
C) 3 < 2 < 4 < 1
D) 4 < 3 < 2 < 1
E) 1 < 2 < 4 < 3

Question 37

How many peaks would you expect in the proton decoupled ¹³C NMR spectrum of 2-pentanol?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 38

A bromoalkane shows two parent ion peaks m/z 122 and 124.What is the molecular formula?

A) C₄H₉Br
B) C₃H₇Br
C) C₂H₅Br
D) CH₃Br
E) C₂H₁₉Br

Question 39

Which compound has five singlets in its proton-decoupled ¹³C NMR spectrum and two quartets, one triplet, one doublet, and one singlet in its proton-coupled ¹³C NMR spectrum?

A)
B)
C)
D)
E)

Question 40

Which of the following molecules shows only one singlet in its ¹H NMR spectrum?

A) I
B) II
C) I and III
D) IV
E) V

Question 41

Which of the following compounds will have a molecular ion of m/z = 114 and a ¹³C NMR spectrum with four peaks?

A)
B)
C)
D)
E)

Question 42

The mass spectrum of 1-pentanol shows an intense daughter ion peak at m/z = 31.This peak could be due to the formation of:

A) C₅H₁₂O^•
B) C₃H₇O⁺
C) CH₃O⁺
D) CH₄O^•
E) C₄H₁₀O⁺

Question 43

Which of the following compounds will have one peak in its ¹H NMR and two peaks in its ¹³C NMR spectrum?

A)
B)
C)
D)
E)

Question 44

An unknown oxygen-containing organic molecule shows a parent peak on its mass spectra at m/z 122.With no information from the visible or uv, the IR revealed major broad absorptions from 2500 cm^-1 to 3500 cm^-1, and strong sharp absorptions at 2930 cm^-1, 1690 cm^-1, and 1230 cm^-1.The ¹H NMR revealed a singlet downfield around $\delta$ 13 (1H) and a multiplet at $\delta$ 7.2 (5H).The molecule consistent with these facts is:

A)
B)
C)
D)
E)

Question 45

An unknown oxygen containing organic molecule shows a parent peak in its mass spectrum at m/z 58.There is no measurable uv or visible spectrum.The IR shows strong, sharp absorptions at 2930 cm^-1 and 1725 cm^-1.The ¹H NMR shows a singlet at $\delta$ 2.1 (6H).Which of the following structures best fits the spectral data?

A)
B)
C)
D)
E)

Question 46

An unknown hydrocarbon shows a parent peak on its mass spectra at m/z 86.There is no evidence of absorptions from visible or uv spectra.The IR shows no major absorptions outside the C-H stretch and bending vibrations.The ¹H NMR reveals a singlet at $\delta$ 0.9 (9H), a triplet at $\delta$ 0.98 (3H), and a quartet at $\delta$ 1.6 (2H).

A)
B)
C)
D)
E)

Question 47

Which of the following compounds will have two peaks in its ¹H NMR spectrum and a broad band in the 3200 to 3500 cm^-1 region of its IR spectrum?

A)
B)
C)
D)
E)

Question 48

A hydrocarbon shows a parent ion peak in its mass spectrum at m/z 102.Its ¹H NMR spectrum shows only two peaks, a singlet at $\delta$ 2.7 (1H) and a multiplet at $\delta$ 7.4 (5H).The correct structure is:

A)
B)
C)
D)
E)