Spectroscopy Analysis

IR: C-H signal

about 3000cm-1 (>sp2, <sp3)

IR: O-H signal

33-3500cm-1 (usually broad and strong; especially for acids)

IR: N-H signal

About 31-3300cm-1 (usually medium, two peaks for NH2)

IR: C triple bond signal

about 2100-2260 (short and weak)

IR: C triple bonded to N signal

about 2250 (usually medium)

IR: C=O signal

about 1700-1750cm-1 for aldehydes, ketones, esters, acids (always strong)

IR: C=C signal

about 1650cm-1 (usually weak)

what molecule usually shows prominent peaks about 1600-1500cm-1

benzene rings

Guide to interpretation of Spectra (about 5 steps)

1. Calculate HDI

2. Examine IR: look for the key 7 signals (all included in flashcards)

3. Account for HDI with groups found in IR; unaccounted IHD value indicates presence of ring

4. Examine H NMR (trends included in flashcards)

   1. assess all signals above 5ppm

   2. identify all methyl groups

   3. identify other multiplets from left to right

HNMR: Hs on Sp3 Cs

anywhere 1-5ppm; EN neighbors occur further downfield

HNMR: alkene Hs

5-8ppm

HNMR: Benzene

6.5-8.5ppm

HNMR: aldehyde

9-10+ppm

HNMR: OH (acid)

10-13ppm

HNMR: terminal alkyne

2.5ppm (rare)

What protons almost always occur as singlets

protons bonded to O, N, S due to “fast exchange” (H moving too fast to be picked up on HNMR)

HNMR: signals representative of methyl group (mostly)

Multiplets of integrations that are multiples of 3

J value = 6-8 Hz

vicinal Hs on sp3 Cs/benzene

J-value = 6-12 Hz

cis-alkene

J-value = 12-18 Hz

trans-alkene