IR Spectroscopy

Question 1

What is the IR stretch of a N-H bond?

Answer 1

3150-3300 cm-1

Question 2

What is the IR stretch for a O-H bond?

Answer 2

3600-3000 cm-1

Question 3

What is the IR stretch for C-H bonds?

Answer 3

3000 cm-1

Question 4

What is the IR stretch for triple bonds e.g. C-C or C-N triple bonds?

Answer 4

2200 cm-1

Question 5

What is the IR stretch for double bonds C=O and C=C?

Answer 5

C=O 1650-1800 cm-1

C=C 1640 cm-1

Question 6

What is the IR stretch for aromatic C=C bonds?

Answer 6

1500-1600 cm-1

Question 7

What is the X-H or single bond region!

Answer 7

4000-2500 cm-1

Question 8

What are there two N-H absorptions?

Answer 8

• Because of symmetrical and antisymmetrical vibrations

* antisymmetric vibrations are slightly lower in energy

Question 9

What effect does increasing s-character have on the C bond strength?

Answer 9

An increasing s-character at C increases the bond strength

Question 10

What is the triple bond region in an IR spectra?

Answer 10

2500-2000 cm-1

Question 11

What is the double bond region?

Answer 11

2000-1500 cm-1

Question 12

What increases the strength of an Alkenes signal?

Answer 12

An Alkene signal is stronger if the Alkene is conjugated (polarisation)

Question 13

What is the carbonyl region?

Answer 13

1800-1650 cm-1

Question 14

What is the key peak of absorbance for a ketone?

Answer 14

1710 cm-1

Question 15

What is the key absorbance for an aldehyde?

Answer 15

1730 cm-1

Question 16

What is the key peak of absorbance for an ester?

Answer 16

1740 cm-1

Question 17

How many signals signify an anhydride and what are the wavenumbers of these peaks?

Answer 17

• there are two signals

* 1820 cm-1 and 1750 cm-1

Question 18

What is the key peak that signifies an acyl chloride?

Answer 18

1790 cm-1

Question 19

What are the main characteristics of increasing bond strength of C=O?

Answer 19

The frequency increased with the electronegativity of the substituents and bond strength increases

Question 20

What is the result of resonance on frequency and bind strength?

Answer 20

Frequency decreases with resonance and bond strength also decreases

Question 21

What is the key peak of absorbance for a conjugated ketone e.g. Acetophenone?

Answer 21

1685 cm-1

Question 22

What is the key peak absorbance of an enone?

Answer 22

1699 cm-1

Question 23

What is the absorbance if a cyclohexanone?

Answer 23

1719 cm-1

Question 24

What is the absorbance of a cyclopentanone?

Answer 24

1740 cm-1

Question 25

What is the absorbance for 3-membered and 4-membered ketone rings?

Answer 25

* 3-membered ring - 1780 cm-1 | * 4-membered ring - 1815 cm-1

Question 26

What is the IR wavenumber for a C-O?

Answer 26

1100 cm-1