[PDF] [PDF] Units used in IR spectroscopy The wavelength of light in the IR

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m The frequency ν in the SI system is measured in reciprocal seconds 1 s − cm or 1 523x10 4 cm -1 We can convert this to Hz by multiplying by the speed 

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electromagnetic conversiton factors is the (exact) pure number 2 997 924 58× 1010 = c0/(cm s-1) The inclusion of non-SI units in this table should not be taken to 

[PDF] Units used in IR spectroscopy The wavelength of light in the IR

cm ν sec-1 = c and E = h ν, then ν = c/ λ; ν is proportional to 1/ λ, the general convention in IR is to list frequencies proportional to energy Frequencies in IR are 

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m-1 Å-1(=1010 m-1) cm-1(=102 m-1) Speed m/s Acceleration m/s2 Diffusion Coefficient Kinematic Viscosity m2/s St(=10-4 m2/s=cm2/s) Power (newton)

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The spectrum can be simulated as coming from an S=1/2 state because the fine structure To convert D, E from Gauss to cm-1 multiply by 4 6686·10-5 · 2 0023

pdf Searches related to cm 1 to s 1

? c Example: The wavelength of the red line in the Hydrogen spectrum is approximately 656 5 nm This corresponds to 656 5 x 10-9 m x 102 cm/m or 656 5 x 10-7 cm or 1 523x104 cm-1 We can convert this to Hz by multiplying by the speed of light which is 2 99792458 x 1010 cm s-1 resulting in 4 566 x 1014 Hz

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Units used in IR spectroscopy

The wavelength of light in the IR region varies from about 2.5 to 40 where 1 = 10 -4 cm. Since cm sec-1 = c and E = h, then = c/ ; is proportional to 1/ ,

the general convention in IR is to list frequencies proportional to energy. Frequencies in IR are generally expressed in 1/ units; ie cm

-1 since these areproportional toenergy.

1/(2.5*10

-4 cm) = 4000 cm -1 ; 1/(40*10 -4 cm) = 250 cm -1

To convert to true energy units, cm

-1 needs to be multiplied by the speed of light, 3*10 -10 cm sec -1, and Planck's Constant, h=6.624*10 -27 erg sec

Infrared Spectroscopy

E vib = (n+1/2)h(k/) .5 /2 ʌwhere = m 1 m 2 /(m 1 +m 2 E rot = J(J+1)h 2 /8 ʌ2I; where I= moment of inertia E vib-rot = (n+1/2)h(k/) .5 /2

ʌ+ J(J+1)h

2 /(8 2 I) n

J= ± 1.

In IR, the change in nis usually by +1, occasionally some + 2 also occurs (overtone). The number of molecules at room temperature that are in an n = 1 state is very small because the energy spacings are large. The rotational energy spacings are considerably smaller; J= ± 1 An example of a molecule with a small moment of inertia: HBr E vib-rot = (n+ 1/2 )h(k/) .5 /2 ʌ+ J(J+1)h 2 /(8 ʌ 2 I) ; where I= moment of inertia n J= ± 1. For most large molecules Iis large. In this spectrum n= +1.

J = ± 1

n =+1 ,J =0 In the condensed phase collision broadening also obcures the n=1, J =0 null A summary of the principle infrared bands and their assignments. R is an aliphatic group.

Funct.

Group Type Frequencie

s cm -1

Peak IntensityExamples Figure No.

C-H sp

3 hybridized R 3

C-H 2850-3000 M(sh) 6, 18, 22

sp 2 hybridized =CR-H 3000-3250 M(sh) 7, 13, 42 sp hybridized

C-H 3300 M-S(sh) 13

aldehyde C-H H-(C=O)R 2750, 2850 M(sh) 14, 15

N-H primary amine, amide

RN-H 2 , RCONH 2

3300, 3340 S,S(br) 18, 19

secondary amine, amid e

RNR-H, RCONHR 3300-3500 S(br) 20, 21

tertiary amine, amide RN(R 3 ), RCONR 2 none 22, 23 O-H alcohols, phenols free O-H 3620-3580 W(sh) 17, 24, 25 hydrogen bonded 3600-3650 S(br) 24, 25, 28 carboxylic acids R(C=O)O-H 3500-2400 S(br) 26, 27, 29, 30 C

N nitriles RCN 2280-2200 S(sh) 31

C

C acetylenes R-CC-R 2260-2180 W(sh) 32

R-CC-H 2160-2100 M(sh) 13

Wavenumbers, cm

-1

5001000150020002500300035004000

% Transmittance

020406080100

CH 3 , CH 2 symmetric and asymmetric stretchesCH 3 , CH 2 bending vibrations(CH 2 4 rock

Figure IR-6.N-Decane, neat liquid, thin film:

CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 sp 3 hybridized CH

Wavenumbers, cm-1

5001000150020002500300035004000

% Transmittance

102030405060708090100

NH 2 bend symmetric and asymmetric NH 2 stretches

Wavenumbers, cm-1

5001000150020002500300035004000

% Transmittance

102030405060708090100

NH 2 bend symmetric and asymmetric NH 2 stretches

Figure IR-18.Butylamine, neat liquid; thin film:

CH 3 CH 2 CH 2 CH 2 NH 2 sp 3 hybridized CH

Wavenumbers, cm

-1

5001000150020002500300035004000

% Transmittance

020406080100

FigureIR-22.Triethylamine, neat liquid; thin film: (CH 3 CH 2 3 N sp 3 hybridized CH A summary of the principle infrared bands and their assignments. R is an aliphatic group.

Funct.

Group Type Frequencie

s cm -1

Peak IntensityExamples Figure No.

C-H sp

3 hybridized R 3quotesdbs_dbs17.pdfusesText_23