Topic 16 IR Spectroscopy

Question 1

Which of the following is not a type of bond vibration?
A. Wag
B. Scissor
C. Bend
D. Twist
E. Stretch

Answer 1

C. Bend

Question 2

Rank the following wavenumbers according to the energy they represent, with 1 = highest energy, and 3 = lowest energy.
A. 2300 cm-1
B. 1200 cm-1
C. 4000 cm-1

Answer 2

C, A, B

Question 3

Rank the following wavelengths according to the energy they represent, with 1 = highest energy, and 3 = lowest energy.
A. 1 cm
B. 500 nm
C. 750 nm

Answer 3

B, C, A

Question 4

What is IR spectroscopy?

Answer 4

A technique that exploits the vibration of covalent bonds to identify how molecules are connected

Question 5

Which two factors influence how fast a bond vibrates?

Answer 5

1. the strength of the bond (strong bond -> high frequency)

2. combined mass of joined atoms (low mass -> high frequency)

Question 6

2 reasons why each functional group has a variation in wavenumber

Answer 6

1. bending and stretching happens at different frequencies

2. Wavelength depends on chemical environment

Question 7

Rank the following bonds according to the wavelength of infra-red light that they absorb, with 1 being the shortest and 3 being the longest: C-O, C-C, C=O

Answer 7

1 = C=O, 2 = C-O, 3 = C-C

Stronger bonds have a higher wavenumber so shorter wavelength (more energy)