Spectroscopy

Question 1

MS

Answer 1

Mass spectroscopy

Measures peaks. Gives molecular mass by m/z ratio.

x axis = m/z
y axis = intensity

Question 2

IR

Answer 2

Infrared spectroscopy

Measures valleys which represent the characteristic absorptions of functional groups from stretching and bending bonds.

x axis = wavelength
y axis = transmittance

Question 3

UV/Vis

Answer 3

Ultraviolet and visible spectroscopy

Excites electrons which promotes them to higher energy orbitals.

Measures peaks which represent the wavelengths that the species absorbs.

x axis = wavelength
y axis = absorption

Question 4

NMR

Answer 4

Nuclear magnetic resonance spectroscopy

x axis = chemical shift (ppm)
y axis = intensity

Question 5

EIMS

Answer 5

Electron impact mass spectroscopy

Forceful ionisation of a molecule into fragments (radicals).

Question 6

Base peak

Answer 6

Largest peak in mass spectroscopy. Assigned 100% intensity.

Question 7

Conjugation

Answer 7

Conjugated molecules (alternating double and single bonds) have strong UV/Vis absorption due to a small HOMO-LUMO gap.

Question 8

Number of signals (1H NMR)

Answer 8

Number of hydrogen environments.

Question 9

Position of signal (1H NMR)

Answer 9

Type of hydrogen environment.

Question 10

Number of signals (13C NMR)

Answer 10

Number of carbon environments.

Question 11

Position of signal (13C NMR)

Answer 11

Type of carbon environment.

Question 12

Intensity of signal (1H NMR)

Answer 12

Number of hydrogens in a signal type.

Question 13

Peak shape (1H NMR)

Answer 13

Number of adjacent hydrogens.

Singlet, duplet, triplet… multiplet following combinatorial coefficients (Pascal’s triangle).

Question 14

DBE

Answer 14

Double bond equivalents

Gives the degree of unsaturation (number of rings and pi bonds) of a structure.

Degree = C + 1 + (N - H - halogens)/2