Chapter 12

Question 1

Frequency of absorption decreases with

Answer 1

Increased atomic mass

Question 2

Frequency of absorption increases with

Answer 2

Increased bond energy

Question 3

A molecule is IR active if

Answer 3

Its movement in the electric field creates a change in dipole (must be polarizable)

Question 4

A molecule is IR inactive if

Answer 4

There is no change in dipole moment, it is either symmetrical or non-polarizable.

Question 5

IR active water molecules stretch in what way?

Answer 5

Asymmetrical stretching, or bending (towards one another)

Question 6

Overtones

Answer 6

Occur with very strong vibrations (c=o) and appear as weak absorptions at double the fundamental frequency.

Question 7

Why do conjugated carbonyl groups vibrate at lower frequencies than non-conjuated carbonyls?

Answer 7

Resonance reduces reduces dipole moment b/c electron density is spread out, which lowers stretch frequency.

Question 8

Why do Nitriles exhibit stronger absorbency (longer spikes) than Alkynes?

Answer 8

C-N bond is more polarizable.

Question 9

Functional Groups that vibrate at frequency of 3300cm^(-1) and appearance.

Answer 9

alcohol (O-H) - broad Amines/amide (N-H) - broad, sharp, or with spikes Alkyne (C-C)- always sharp, usually strong

Question 10

Functional Groups that vibrate at frequency of 3000cm^(-1) and appearance.

Answer 10

Alkane (C-H) - just below 3000 Alkene (C=H) - just above 3000 Acid (O-H) - very broad

Question 11

Functional Groups that vibrate at frequency of 2200cm^(-1)

Answer 11

Alkyne (C=-H) - just below 2200 Nitrile (C=-N) - just above 2200

Question 12

Functional Groups that vibrate at frequency of 1710cm^(-1) (very strong)

Answer 12

Carbonyls: ketones and acids: 1710 aldehydes: 1725 + 2700,2800 esters: 1735 + 2500-3500

Question 13

Functional Groups that vibrate at frequency of ~1685cm^(-1) and appearance.

Answer 13

conjugated carbonyls: ketones: 1685 aldehydes: 1690 acids: 1687

Question 14

Functional Groups that vibrate at frequency of 1660cm^(-1)

Answer 14

conjugated alkenes inimes (C=N) - stronger than C=C amide (C=O group)

Question 15

Functional Groups that vibrate at frequency of 1600cm^(-1)

Answer 15

Aromatic C=C bonds

Question 16

Functional Groups that vibrate at frequency of 1000-1200cm^(-1)

Answer 16

C-O bonds of ethers, esters, and alcohols.

Question 17

quaternary

Answer 17

Question 18

methine C-H

Answer 18

Question 19

methylene CH₂

Answer 19

Question 20

methyl CH₃

Answer 20

Question 21

Answer 21

quaternary

Question 22

Answer 22

methine C-H

Question 23

Answer 23

methylene CH₂

Question 24

Answer 24

methylene CH₂