Transcript OPTICAL ISOMERISM - CHEMSHEETS.co.uk
© www.chemsheets.co.uk AS 062 12-Jul-12
• Light is one form of electromagnetic radiation. • Light is only a very small part of the electromagnetic spectrum.
• Electromagnetic waves consist of electric and magnetic fields which are perpendicular to each other and to the direction of travel of the wave. • The electric and magnetic fields vibrate at the same frequency as each other.
THE ELECTROMAGNETIC SPECTRUM
Atoms, molecules and ions can absorb (or emit) electromagnetic radiation of specific frequencies, and this can be used to identify them.
Electromagnetic radiation absorbed What the energy is used for Spectroscopy technique
Ultra-violet / visible Movement of electrons to higher energy levels Ultra-violet / visible spectroscopy Infra-red Microwaves To vibrate bonds To rotate molecules Infra-red spectroscopy Microwave spectroscopy Radio waves To change nuclear spin NMR spectroscopy © www.chemsheets.co.uk AS 062 12-Jul-12
INFRA-RED SPECTROSCOPY
• All bonds vibrate at a characteristic frequency.
• There are different types of vibration.
Symmetric stretch Assymmetric stretch Bending • The frequency depends on the mass of the atoms in the bond, the bond strength, and the type of vibration. • The frequencies at which they vibrate are in the infra-red region of the electromagnetic spectrum.
INFRA-RED SPECTROSCOPY
• If IR light is passed through the compound, it will absorb some or all of the light at the frequencies at which its bonds vibrate. • Wavenumbers (cm -1 ) are used as a measure of the wavelength or frequency of the absorption.
Wavenumber = 1 wavelength (cm) • IR light absorbed is in the range 4000 – 400 cm -1 .
• Above 1500 cm -1 is used to identify functional groups.
• Below 1500 cm -1 is used for fingerprinting.
© www.chemsheets.co.uk AS 062 12-Jul-12
BELOW 1500 cm
-1
– “Fingerprinting”
• • • Complicated and contains many signals – picking out functional group signals difficult. This part of the spectrum is unique for every compound, and so can be used as a "fingerprint". This region can also be used to check if a compound is pure. © www.chemsheets.co.uk AS 062 12-Jul-12
CH 2 C CH 3 CH 2 CH 3 CH 3 C CH CH 3 CH 3
cyclohexane
C–H
cyclohexene
C–H
butanal
O CH 3 CH 2 CH 2 C H C–H
ethanoic acid
CH 3 O C O H O–H
ethanol
CH 3 CH 2 O H O–H
butanal
O CH 3 CH 2 CH 2 C H C=O
propanone
CH 3 O C CH 3 C=O
ethanoic acid
CH 3 O C O H C=O
methyl ethanoate
CH 3 O C O CH 3 C=O
CH 3 CH 2 O H
Exercise 1
Match the following eight compounds to the following eight IR spectra.
hex-2-ene pentane methylpropan-1-ol 2-methylpentan-3-one butanal butanoic acid propyl ethanoate nitrobenzene
6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 9 5 9 0 8 5 8 0 7 5 7 0
2 5 2 0 1 5 1 0 4 000
3 000 3 500
2 500 2 000 W ave num bers (c m-1 ) 1 500
1 000
5 00
6 5 6 0 5 5 5 0 4 5 4 0 3 5 9 5 9 0 8 5 8 0 7 5 7 0 3 0 2 5 2 0
1 5 1 0 4 000
3 000
3 500
2 500 2 000 W ave num bers (c m-1 ) 1 500
1 000
5 00
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
1 500 1 000 5 00 2 500 2 000 W ave num bers (c m-1 )
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
1 500 1 000 5 00 2 500 2 000 W ave num bers (c m-1 )
6 0 5 5 5 0 4 5 4 0 3 5 9 5 9 0 8 5 8 0 7 5 7 0 6 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
1 500 1 000 5 00 2 500 2 000 W ave num bers (c m-1 )
5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 3 500 3 000
2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
1 000 5 00 2 500 2 000 W ave num bers (c m-1 )
1 500
propyl ethanoate
O CH 3 C O CH 2 CH 2 CH 3 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
C=O 2 500 2 000 W ave num bers (c m-1 ) C-O 1 500 1 000 5 00
2-methylpentan-3-one
CH 3 CH 3 O CH C CH 2 CH 3 6 5 6 0 5 5 5 0 4 5 4 0 3 5 9 5 9 0 8 5 8 0 7 5 7 0 3 0 2 5 2 0 1 5 1 0
4 000
3 000 3 500
C=O 2 500 2 000 W ave num bers (c m-1 ) 1 500
1 000
5 00
methylpropan-1-ol
CH 3 CH 3 CH CH 2 OH 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 O-H 3 000
2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
nitrobenzene
NO 2 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
C-H 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
pentane
CH 3 CH 2 CH 2 CH 2 CH 3 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0
4 000
3 000 3 500
C-H 2 500 2 000 W ave num bers (c m-1 ) 1 500
1 000
5 00
butanal
O CH 3 CH 2 CH 2 C H 6 0 5 5 5 0 4 5 4 0 3 5 9 5 9 0 8 5 8 0 7 5 7 0 6 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000
C-H C=O 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
butanoic acid
O CH 3 CH 2 CH 2 C O H 5 0 4 5 4 0 3 5 3 0 2 5 2 0 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 1 5 1 0
4 000
O-H
3 000 3 500
2 500 2 000 W ave num bers (c m-1 ) 1 500
1 000
5 00
hex-2-ene
CH 3 CH CH CH 2 CH 2 CH 3 5 0 4 5 4 0 3 5 3 0 2 5 2 0 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 C-H 1 5 1 0
4 000
3 000 3 500
C-H C=C 2 500 2 000 W ave num bers (c m-1 ) 1 500
1 000
5 00
F
9 5 9 0 8 5 8 0 7 5 7 0 4 5 4 0 3 5 3 0 6 5 6 0 5 5 5 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
G
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
9
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
10
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
11
9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 4 000 3 500 3 000 2 500 2 000 W ave num bers (c m-1 ) 1 500 1 000 5 00
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