IR INTERPRETATION

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IR INTERPRETATION

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Infra red spectra interpretation : 

Infra red spectra interpretation 1 D LOHITHASU M PHARM

CONTENT : 

CONTENT IR SPECTROSCOPY THEORY OF ABSORPTION MODES OF VIBRATIONS INFRA RED SPECTRA SPECTRA OF FEW COMPOUNDS 2

IR SPECTROSCOPY : 

IR SPECTROSCOPY Infrared (IR) absorption spectroscopy is the measurement of the wavelength and intensity of the absorption of mid-infrared light by a sample. The IR spectrum of a sample is fingerprint for its identification as each functional group gives its characteristic spectrum. 3

IR SPECTRUM RANGE : 

IR SPECTRUM RANGE IR Region range 4

THEORY OF IR ABSORPTION : 

THEORY OF IR ABSORPTION 5 For a molecule to absorb IR radiations , the vibrations or rotations with in a molecule must cause a net change in dipole moment of the molecule. The alternating electrical field of the radiation interact with fluctuations in dipole moment of the molecule. If the frequency of the radiation matches with the vibration freqency of the molecule then radiation will absorb, causing change in amplitude of the molecule vibration.

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6 Transitions involved in IR absorption are associated with vibrational changes with in the molecule. Each different vibration modes may give to different absorption bands. IR spectroscopy is therefore basically termed as vibrational spectroscopy.

MODES OF VIBRATIONS : 

MODES OF VIBRATIONS 7 There are two types of vibrations: Stretching: These type of vibrations involve movement of atom within the same bond axis, such that bond length changes without any change in the bond . 2) Bending: These type of vibrations involve movement of atom which are attached to a common central atom such that there is change in the in bond axis and bond angle of each individual atom without any change in the bond length. Stretching type of vibration is further divided into two types a) Symmetrical: these type of vibrations the two atoms move away or towards the central atom, without any change in bond axis or bond angle.

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8 b) Asymmetrical vibration: These type of vibrations the atoms move with respect to central atom such that one moves away and the other moves towards the central atom. Bending vibrations are further divided four types a) scissoring vibrations: In these type of vibrations, in plane bending of atoms wherein they move back and fourth.

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9 b) Rocking vibrations: These type of vibrations ,in plane bending of atoms occur wherein they swing back and fourth with respect to central atom. c) Wagging vibrations: In these type of vibrations , out of plane bending of the atoms occur wherein they oscillate back and fourth.

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d) Twisting vibrations: In these type of vibrations, out of plane bending of atoms occur wherein they rotate around the bond which joins the central of the molecule. 10

INFRA RED SPECTRA : 

INFRA RED SPECTRA When infra red light is passed through a sample of organic compound some of the frequencies are absorbed, while others are transmitted without any absorption. If we plot absorbance or transmittance against frequency, the result is an infra red spectrum. 11

IR REGION IS DIVIDED INTO : 

IR REGION IS DIVIDED INTO 12 Group frequency region 4000 - 1500 cm-1 Finger print region 1500 - 400 cm-1 Of the above two regions, finger print region is the most useful region in interpretation of the functional groups .

3600-2700 cm-1X-H stretch region : 

3600-2700 cm-1X-H stretch region 13

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2300 – 2100 cm-1 : 

2300 – 2100 cm-1 15

1850-1500 cm-1 C=X stretch region : 

1850-1500 cm-1 C=X stretch region 16

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1500-400 cm-1Fingerprint Region : 

1500-400 cm-1Fingerprint Region 19

Ethanoic acid spectrum : 

Ethanoic acid spectrum Ethanoic acid has the structure: You will see that it contains the following bonds: carbon-oxygen double, C=O carbon-oxygen single, C-O oxygen-hydrogen, O-H carbon-hydrogen, C-H carbon-carbon single, C-C 20

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The carbon-oxygen double bond, C=O, is one of the really useful absorptions, found in the range 1680 - 1750 cm-1  The O-H bond this absorbs differently depending on its environment. It is easily recognised in an acid because it produces a very broad trough in the range 2500 - 3300 cm-1. The C-H bond absorbs somewhere in the range from 2853 - 2962 cm-1. 22

Ethanol spectrum : 

Ethanol spectrum Ethanol has the structure: oxygen-hydrogen, O-H carbon-hydrogen, C-H carbon-carbon single, C-C 23

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The O-H bond in an alcohol absorbs at a higher wavenumber than it does in an acid - somewhere between 3230 - 3550 cm-1  the absorption due to the C-H bonds just under 3000 cm-1, and also the troughs between 1000 and 1100 cm-1 - one of which will be due to the C-O bond. 25

Ethyl ethanoate spectrum : 

Ethyl ethanoate spectrum Ethyl ethanoate has the structure: carbon-oxygen double, C=O carbon-oxygen single, C-O carbon-hydrogen, C-H carbon-carbon single, C-C 26

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The presence of the C=O double bond is seen at about 1740 cm-1. The C-O single bond is the absorption at about 1240 cm-1. 28

Propanone spectrum : 

Propanone spectrum Propanone has the structure carbon-oxygen double, C=O carbon-hydrogen, C-H carbon-carbon single, C-C There is a marked absorption at about 1700 cm1due to the C=O. 29

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1-HEXENE SPECTRUM : 

1-HEXENE SPECTRUM 1-Hexene has the structure Carbon-carbon double, C=C carbon-hydrogen, C-H carbon-carbon single, C-C 31

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The spectrum has the various CH stretch bands that all hydrocarbons show near 3000 cm-1. There is a weak alkene CH stretch above 3000 cm-1. There is an out-of-plane CH bend for the alkene in the range 1000-650 cm-1. There is also an alkene CC double bond stretch at about 1650 cm-1 . 33

IR SPECTRUM OF OCTANE : 

IR SPECTRUM OF OCTANE Octane has structure carbon-hydrogen, C-H carbon-carbon single, C-C 34

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C–H stretch from 3000–2850 cm-1 C–H bend or scissoring from 1470-1450 cm-1 C–H rock, methyl from 1370-1350 cm-1 C–H rock, methyl, seen only in long chain alkanes, from 725-720 cm-1 36

1-BROMO BUTANE : 

1-BROMO BUTANE 1-Bromo butane has structure carbon-hydrogen, C-H carbon-carbon single, C-C carbon-Bromine ,C-Br 37

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The spectrum for 1-bromobutane, C4H9Br, is shown here. The CH stretch still appears at about 3000 cm-1. The CH2 bend shows up near 1400 cm-1, and the CBr stretch band at approximately 700 cm-1. 39

BENZENE SPECTRUM : 

BENZENE SPECTRUM Benzene has structure carbon-hydrogen, C-H carbon-carbon single, C-C carbon-carbon double, C=C 40

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The IR spectrum for benzene, C6H6, has only four prominent bands because it is a very symmetric molecule. Every carbon has a single bond to a hydrogen. Each carbon is bonded to two other carbons and the carbon-carbon bonds are alike for all six carbons. The molecule is planar. The aromatic CH stretch appears at 3100-3000 cm-1 There are aromatic CC stretch bands (for the carbon-carbon bonds in the aromatic ring) at about 1500 cm-1. Two bands are caused by bending motions involving carbon-hydrogen bonds. The bands for CH bends appear at approximately 1000 cm-1 for the in-plane bends and at about 675 cm-1 for the out-of-plane bend. 42

SPECTRUM OF TOLUENE : 

SPECTRUM OF TOLUENE Toluene has structure carbon-hydrogen, C-H carbon-carbon single, C-C carbon-carbon double, C=C 43

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C–H stretch from 3100-3000 cm-1 overtones, weak, from 2000-1665 cm-1 C–C stretch (in-ring) from 1600-1585 cm-1 C–C stretch (in-ring) from 1500-1400 cm-1 C–H "oop" from 900-675 cm-1 45

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