Deck 12: Molecular Characterisation

Question 1

By elemental analysis, the carbon content of an unknown compound was found to be 85.7%. From the following molecular formulae, (a)-(d), pick out the most likely formula for this unknown compound:

A) C₄H₈O
B) C₅H₈O
C) C₆H₁₂
D) C₆H₆

Answer 1

C

Question 2

Pick out the isotopic distribution pattern for 2-phenylpropanoic acid (hint: 1.1% of all carbon atoms have an atomic mass of 13).

A) 150 (M, 100%), 151 (1%), 152 (0.01%).
B) 150 (M, 100%), 151 (5%), 152 (0.05%).
C) 150 (M, 100%), 151 (10%), 152 (0.1%).
D) 150 (M, 100%), 151 (20%), 152 (0.2%).

Answer 2

C

Question 3

Pick out the molecular ion peak for a molecule containing a single nitrogen atom.

A) 84.
B) 93.
C) 108.
D) 114.

Answer 3

B

Question 4

Match the following molecular formulae to the mass spectra A-C:

-C₇H₇Br

A) B
B) C
C) A

Question 5

Match the following molecular formulae to the mass spectra A-C:

-C₈H₉NOCl

A) B
B) C
C) A

Question 6

Match the following molecular formulae to the mass spectra A-C:

-C₁₀H₂₁NO

A) B
B) C
C) A

Question 7

Which of the following bonds has the strongest IR absorption?

A) A.
B) B.
C) C.
D) D.

Question 8

Match the following aliphatic molecules to their infrared carbonyl stretching frequency:

-1815 cm^-1

A) A
B) C
C) D
D) B

Question 9

Match the following aliphatic molecules to their infrared carbonyl stretching frequency:

-1740 cm^-1

A) A
B) C
C) D
D) B

Question 10

Match the following aliphatic molecules to their infrared carbonyl stretching frequency:

-1715 cm^-1

A) A
B) C
C) D
D) B

Question 11

Match the following aliphatic molecules to their infrared carbonyl stretching frequency:

-1650 cm^-1

A) A
B) C
C) D
D) B

Question 12

From the following molecules, pick out those which have no infrared absorption for a symmetrical stretch involving their corresponding double/triple bond(s). Please select all that apply.

A) A.
B) B.
C) C.
D) D.

Question 13

From the following molecules, pick out those which have four proton signals in their ¹H NMR spectrum. Please select all that apply.

A) A.
B) B.
C) C.
D) D.
E) E.

Question 14

From the following molecules, pick out those which do not have four proton signals in their ¹H NMR spectrum. Please select all that apply.

A) A.
B) B.
C) C.
D) D.
E) E.

Question 15

How many magnetically non-equivalent carbon atoms are there in toluene?

A) 4.
B) 5.
C) 6.
D) 7.

Question 16

How many magnetically non-equivalent carbon atoms are there in the following molecule?

A) 5.
B) 8.
C) 4.
D) 6.

Question 17

How many magnetically non-equivalent carbon atoms are there in the following molecule?

A) 7.
B) 8.
C) 10.
D) 11.
E) 13.

Question 18

From the following molecules, pick out those which have six carbon signals in their ¹³C NMR spectrum. Please select all that apply.

A) A.
B) B.
C) C.
D) D.
E) E.

Question 19

For an unknown compound, its proton and carbon NMR spectra showed three proton and four carbon signals, respectively. Pick out this unknown compound from the following molecules.

A) A.
B) B.
C) C.
D) D.

Question 20

The following molecules were examined by ¹H NMR spectroscopy. Rank them in order of decreasing chemical shift for their methyl group (where 1 indicates the largest ppm and 3 indicates the smallest ppm):

A) Molecule A
B) Molecule B
C) Molecule C

Question 21

Which one of the following ¹H NMR signals is a quintet?

A) A.
B) B.
C) C.
D) D.

Question 22

By ¹H NMR spectroscopy, what is the expected signal intensity for the eight lines of an octet?

A) 1:1:1:1:1:1:1:1.
B) 1:2:3:4:4:3:2:1.
C) 1:3:6:12:12:6:3:1.
D) 1:5:10:15:15:10:5:1.
E) 1:7:21:35:35:21:7:1.

Question 23

How many degrees of unsaturation are there in a compound with the molecular formula C₆H₁₀NOCl?

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

Question 24

An unknown compound is analysed using NMR spectroscopy, generating the NMR spectra shown below. What is the structure of the unknown compound?

¹H NMR spectrum of unknown compound

¹³C NMR spectrum of unknown compound

¹H NMR expansion 1

¹H NMR expansion 2

A) A.
B) B.
C) C.
D) D.

Question 25

An unknown compound is analysed using NMR spectroscopy, generating the NMR spectra shown below. What is the structure of the unknown compound?

¹H NMR spectrum of unknown compound

¹³C NMR spectrum of unknown compound

¹H NMR expansion 1

¹H NMR expansion 2

¹H NMR expansion 3

A) A.
B) B.
C) C.
D) D.

Question 26

Select all of the following statements on expected IR frequencies that are true. Please select all that apply.

A) Acid chlorides will appear between 1820 - 1650 cm^-1
B) Esters will appear between 3600 - 2500 cm^-1
C) Phenols will appear between 3600 - 2500 cm^-1
D) Aromatic C-H will appear between 3000 - 2850 cm^-1

Question 27

Select the following analytical techniques that would allow a pair of enantiomers of a molecule to be distinguished. Please select all that apply.

A) Chiral liquid chromatography
B) Mass Spectrometry
C) ¹H-NMR
D) Polarimetry

Question 28

Select the molecule from the following structure that will have 6 carbon peaks, 4 hydrogen peaks in its NMR spectra.

A) A
B) B
C) C
D) D

Question 29

Based on the information given, select the molecule to which it fits best.
7 carbon and 5 hydrogen peaks in its NMR spectra. MS 183.95 (100 %), 185.95 (100 %). IR frequency at 1740 cm^-1

A) A
B) B
C) C
D) D

Question 30

Select the two major factors which influence chemical shifts from the list below. Please select all that apply.

A) Electron density
B) Anisotropic effects
C) Symmetry effects
D) Number of adjacent atoms