Chem 2325

Unit 1

As the atoms get heavier, the frequency ___

decreases E=hv

Frequency decreases with ___-

Increasing atomic mass E=hv

Frequency increases with

bond energy ( as the bond gets stronger, the frequency increases) E=hv

What bonds only display bands in the IR spectrum

Only polar bonds - dipole moment

Strong polar bonds such as carbonyl groups (C=O) produce ___

Strong bands in IR spectrum

Medium polarity bonds and asymmetric bonds produce ____

medium bands

Weakly polar bonds and symmetric bonds produce ___

weak or non observable bonds

Conjugation increases/decreases the frequency

it decreases; lowers the energy

as the percent of s-character of the carbon hybrid orbitals increases, the CH bond becomes ___

stronger and the stretching frequency increases. sp3 -2800-300 cm^-1 (1s/4p). sp- 3300cm-1 (1s/1p)

IR spectrum of alkanes characteristics

-no functional groups

-only c-c and c-h

-only C-H will appear ( polar) around 3000cm^-1

IR spectrum of terminal alkenes characteristics

-C=C bond stretching vibration at 1600-1700 cm^-1

-might show =C-H bond stretch around 3080 cm^-1

IR spectrum of internal alkenes characteristics

• =C-H around 3080 cm^-1 can be obscured by the broader bands appearing around 3000 cm^-1

• internal alkene is less polar than terminal alkene, meaning the band is less intense

IR spectrum of alkynes characteristics

-sharp, weak band around 2100 cm^-1 (triple bond is not very polar)

-the bond doesn’t show at all in highly symmetrical alkynes

- terminal alkynes- triple bond at the end of a carbon chain. the C-H bond may show a sharp, weak band at 3300cm^-1

-internal alkynes - triple bond in the middle of a carbon chain. No C-H bonds to the sp carbon so not visible band.

IR spectrum C-N bond frequency

1200 cm^-1 (usually strong bands)

IR spectrum C=N bond frequency

1660 cm^-1 (usually strong bands)

IR spectrum C triple bond N bond frequency

more than 2200 cm^-1 (usually strong bands)

IR spectrum C triple bond N bond frequency

less than 2200cm^-1 ( usually moderate or weak)

IR spectrum of a nitrile caracteristics

-C triple bond N around 2250 cm^-1

-pointed shape, sharp

IR spectrum of an alcohol characteristics

• O-H bond, strong and broad around 3000-3700 cm^-1

IR spectrum of aldehydes and ketones characteristics

• aldehydes at the end of a carbon chain, two peaks 2700-2800 cm^-1, 1726cm^-1

• ketones at in the middle of the chain, one peak 1710 cm^1

• Both show a strong, prominent band around 1710-1720 cm^-1

• aldehydes show a pair of medium strength bands around 2700-2800 cm^-1 ——- this is not shown in the ketones

IR spectrum of carboxylic acids characteristics

• carboxylic acids will show two peaks. 1710, 2500-3500cm^-1

• very strong and broad band at 2500-3500cm^-1

• C=O bond at 1710cm^-1

• Conjugated carbonyl compounds 1685cm^-1

• Esters around 1735cm^-1 (RCOOR’)

• strained cyclic ketones at a higher frequency above 1725cm^-

IR spectrum of amines characteristics

• weak, medium, somewhat broad at 3200-3600 cm^-1. but not as bad as OH

• primary amines have 2 N-H bonds — broad N-H stretching around 3300cm^-1

• secondary amines have only one N-H bond — one spkie around 3300cm^-1

• tertiary amines have no N-H bonds so not shown in IR spectrum

IR spectrum of amides characteristics

• N-H stretch around 3100-3500 cm^-1

• C=O band lower than 1710 cm^-1 due to conjugation

MS. If Br is present, the intensity of M+2 peak is

almost equal to M+

MS. If Cl is present, the intensity of M+2 peak is

1/3 of M+1

MS. If an odd number of nitrogen atoms are present, M+

will be an odd number

MS. if iodine is present,

there is a peak at 127, and a large gap to the next smaller peak