spectroscopy quick memorization

Electromagnetic Radiation Equations

c=\lambda\nu

E = hv = \frac{hc}{\lambda}

Wave number

1 / lambda

FG region

>/= to 1500 cm-1

Fingerprint Region

< 1500cm-1

Hooke’s Law

frequenct wavenumber =

k\sqrt{\frac{f}{m}}

stronger (f) bond = higher frequency

smaller mass = higher frequency

Increasing Wavenumber and Energy Trend (right to left)

single bonds < double bonds < triple bonds < bonds to HYDROGEN

O-H absorption

3600-3200

strong broad

N-H absorption

3500-3200

medium

C-H absorption

~3000

• Csp³-H = 3000-2850 strong

• Csp²-H = 3150-3000 medium

• Csp-H = 3300 medium

CC TRIPLE bond

• 2250 medium

CN TRIPLE bond

• 2250 medium

CO DOUBLE bond

• 1800-1650 (often 1700)

• strong

CC DOUBLE bond

1650

medium

Benzene ring

• 1600,1500

• medium

Effect of sp character on CH absorptions

Bond Strength and Wavenumber INCREASES with HIGHER % s-character

Alkanes

• only CC bonds

• sp³ hybridized C atoms = 3000-2850 (strong)

Alkenes

• Csp²—H = 3150-3000 (medium)

• Csp³—3000-2850 (strong)

• CC Double = 1650 (medium)

Alkynes

• Csp—H = 3300 (medium)

• Csp³—H = 3000-2850 (strong)

• CC Triple = 2250 (medium)

Aromatic Compounds with Benzene rings

• Csp²—H = 3150-3000 (medium)

• Csp³—H = 3000-2850 (strong)

• Benzene ring = 1600,1500 (medium)

Alcohols

• OH group at 3600-3200 (strong, broad)

Ethers

• Csp³—H = 3000-2850 (strong)

• Compounds that contain an oxygen atom but do NOT show an OH or C=O absorption are ethers

Aldehydes

• C=O at 1700 (strong)

• Csp²—H of CH = 2830-2700

• Csp³—H = 3000-2850 (strong)

Ketones

• Csp³—H = 3000-2850 (strong)

• C=O = 1700 (strong)

Shifts to higher wavenumber when SIZE of the ring DECREASES

Carboxylic Acids

O-H = 3500-2500 (broad,strong)

C=O = 1700 (strong)

Esters

• Csp³—H = 3000-2850 (strong)

• C=O = 1700 strong

Amide

• N—H = 3400-3200 (1 or 2 peaks)

• C=O = 1700 (strong)

• N-H = 1700 (medium)

Amines

• N-H:

  • 3300

  • 3400

Nitriles

• triple bond region: 2250 (medium)

• NH = 3500-3300

Chemical Shift Equation

• observed chemical shift downfield from TMS / v of the NMR spectrometer (MHz)

• 1 MHz = 10^6 Hz

Chemical shift values

RCH3 = 0.9

R2CH2 = 1.3

R3CH = 1.7

Z=VH = 1.5-2.5

triple bond H = 2.5

ZR2CH = 2.5-4

RY=\H = 4.5-6

benzene ring = 6.5-8

RO=CH = 9-10

RO=COH = 10-12

ROH or RNH = 1-5