IR spectrometry and mass spectroscopy

Question 1

effect of IR radiation on covalent bonds

Answer 1

the covalent bonds will bend (change in bond angle) or stretch (change in distance between atomic centres)

Question 2

three main greenhouse gases

Answer 2

water vapour, carbon dioxide, methane. they absorb longer wavelength IR radiation because it has the same frequency as the natural frequency of their bonds

Question 3

how to identify alcohols from O-H absorption peaks

Answer 3

3200-3600
broad

Question 4

how to identify aldehydes and ketones from C=O absorption peaks

Answer 4

1630-1820
narrow

Question 5

how to identify carboxylic acids from C=O and O-H absorption peaks

Answer 5

1630-1820 (C=O)
2500-3330 (O-H)
broad

Question 6

uses of IR spectroscopy

Answer 6

monitor air pollution: remote sensors analyse IR spectra of vehicle emissions
breathalysers: based on the IR spectrum of ethanol

Question 7

define molecular ion

Answer 7

the positive ion formed when a molecule loses an electron

Question 8

define M+ peak

Answer 8

clear peak at the highest m/z value on the right hand side of the mass spectrum (equal to Mr)

Question 9

what is the M+1 peak?

Answer 9

a small peak after the M+ peak which exists because 1.1% of carbon is present as the carbon-13 isotope

Question 10

fragmentation peaks

Answer 10

formed by fragment ions (formed from breakdown of a molecular ion by fragmentation)
CH3+. 15
C2H5+ 29
C3H7+ 43
C4H9+. 57