Question

When a molecular formula is given, it is advisable to calculate an indo (Section 1.4). The index often gives useful information about the functional group or groups that 1. In each of the following parts, a molecular formula is given. Deduce the structure that is con- sistent with the infrared spectrum. There may be more than one possible answer. PROBLEMS may be present in the molecule. (a) CHCI 15 125 pomin C3H2CI 3600 3200 2600 2400 2000 1200 1000 BOO 000 1000 WENUMBERSIC (b) CH4 $ 88 8888888 CHIA 40 30 20 1900 140 o 4000 1500 300 600 (c) CHO CyH2O 2000 10 VVENUMBERS OU

Answer 1

н | a) C3H3CI Degree of unsaturation (or IHD) = (2C+2)+N-H-X)/2 = (8-4)/2 = 2 IR: 3200: terminal alkyne sp C-H stretching sharp 2980: sp3 C-H stretching 2220: alkyne CEC stretching H-C=C—C—CI 1400: CH2 scissoring 1280: C-Cl stretching Н. Thus possible compound is: 3-chloroprop-1-yne b) C10H14: Degree of unsaturation (or IHD) = ((2C+2)+N-H-X)/2 = (22-14)/2 = 4 There is a possible aromatic ring accounting for these four sites of unsaturation. IR: CH3 3010: sp2 C-H stretching 2960: sp3 C-H stretching 1610: aromatic C=C stretching 1520: CH3 rocking 1450: CH2 scissoring 830: OOP para substitution Thus the possible compound is: 1,4-diethylbenzene H3C

c) C7H80: Degree of unsaturation (or IHD) = ((2C+2)+N-H-X)/2 = (16-8)/2 = 4 There is a possible aromatic ring accounting for these four sites of unsaturation. IR: 3400:-OH stretching ОН 2990: sp3 C-H stretching 1600: aromatic C=C stretching 1480: CH3 rocking 840: OOP para substituted aromatic ring Thus the possible compound is: 4-methylphenol CH3

Please note that using only IR spectrum alone we can give possible structure. However, to elucidate complete structure additional NMR, mass spectrum are needed.