IR Spectroscopy

Question 1

Larger frequencies (higher energies) are absorbed by…

Answer 1

-Bonds with a higher bond order
-Bonds between atoms with a larger mass difference

Question 2

What is the critical reference value for the N-H/O-H region?

Answer 2

3250 cm-1

Question 3

How do we differentiate between peaks in the N-H/O-H region?

Answer 3

-O-H peaks are typically strong to moderate and broad
-N-H peaks are typically moderate to weak and sharp
-C-H peaks are very sharp

Question 4

What is the critical reference value for the C-H region?

Answer 4

3000 cm-1

Question 5

How do you differentiate between peaks in the C-H region?

Answer 5

-sp3 is to the right of 3000
-sp2 is to the left of 3000
-Aldehyde is 2750 and 2850

Question 6

What is the critical reference value for the C triple bond N/C triple bond C region?

Answer 6

2250 cm-1

Question 7

How do you differentiate between peaks in the C triple bond N/C triple bond C region?

Answer 7

-Alkyne peaks are moderate to weak
-Nitrile peaks are strong to moderate

Question 8

What is the critical reference value for the C=O region?

Answer 8

1715 cm-1

Question 9

What is the range possible for C=O?

Answer 9

1800-1650

Question 10

How do you differentiate peaks in the C=O region?

Answer 10

C=O peaks are typically strong and slightly broad

Question 11

What is the critical reference value for the C=C region?

Answer 11

1600 cm-1

Question 12

How do you differentiate between peaks in the C=C region?

Answer 12

-C=C peaks are typically strong to moderate and sharp
-Aromatic C=C is below 1600 cm-1
-Alkene C=C is above 1600 cm-1

Question 13

What are critical reference values?

Answer 13

Center value of the FG range

Question 14

List the approximate zone lines from left to right.

Answer 14

3200, 2700, 2000, 1650, 1400

Question 15

What is the critical reference value for the C=O FG region?

Answer 15

1715 cm-1

Question 16

How do you differentiate between peaks in the C=O region?

Answer 16

-Aldehyde has present of moderate C-H peak (2x below 3000)
-Carboxylic acid has presence of extremely broad O-H peak

Question 17

Ester _____ vibrational energy by _____.

Answer 17

increases, 30 cm-1

Question 18

Amide ______ vibrational frequency by _____.

Answer 18

decreases, 30 cm-1

Question 19

Acyl halides/anhydrides ______ energy more than ____.

Answer 19

increase, 30

Question 20

Conjugation decreases vibrational frequency by ______.

Answer 20

30 cm-1

Question 21

Conjugation on both sides of the carbonyl decreases frequency by _____.

Answer 21

60 cm-1

Question 22

_______ is strain free and “normal”.

Answer 22

cyclohexane

Question 23

Ring strain increases vibrational energy by ______.

Answer 23

30 cm-1

Question 24

More strain = ______.

Answer 24

higher energy

Question 25

What is the stretching frequency of an anhydride?

Answer 25

1810 cm-1

Question 26

What is the stretching frequency of an acid chloride?

Answer 26

1800 cm-1

Question 27

What is the stretching frequency of an ester?

Answer 27

1735 cm-1

Question 28

Resonance causes the bond to _____ and induction causes the bond to ______.

Answer 28

lengthen, shorten