Orgo chapter 11 mcat

Infrared spectroscopy/ IR spectroscopy

measures absorption of infrared light, which caused molecular vibration (stretching, bendingh, twising, folding)

O H peak

broad peak between 3300 and 3000

N H peak

sharp peak around 3300

C=O peak

sharp peak at 1750

UV spectroscopy

most useful for studying compounds containing double bonds or heteroatoms with lone pairs that create conjugate system

proton NMR

best used for:

• determining relative number og protons and their relative chemical environments

• showing how many adjacent protons there are by splitting patterns

• inferring certain functional groups

alkyl groups

0 to 3 ppm

alkynes

2-3 ppm

alkenes

4.6-6 ppm

aromatics

6-8.5 ppm

aldehydes

9-10 ppm

carboxylic acids

10.5-12 ppm

nuclear magnetic resonance spectroscopy/ NMR spectroscopy

measures alignment of nuclear spin with an applied magnetic field, which depends on the magnetic environment of the nucleus itself. It is useful for determining the structure (connectivity) of a compound, including functional groups

deshielding

occurs when EWG pull electron density away from the nucleus, allowing it to be more easily affected by the magnetic field, this moves peaks further downfield

left/downfield

higher chemical shifts are located where?

right/upfield

lower chemical shifts are located where?

linear

Bond angle: 180

Steric number: 2

trigonal planar

Bond angle: 120

Steric number: 3

tetrahedral

Bond angle: 109.5

Steric number: 4