Infrared presentation

Infrared Spectroscopy

Spectroscopy is the measurement of the absorption or emission of energy by matter (atoms or molecules)when it is subjected to electromagnetic radiation.

A spectrophotometer measures the energy changes that take place within a molecule when it is irradiatedand records these changes as spectra.

In absorption spectroscopy, molecules absorb energy and undergo transitions from the ground state to an excited state of the molecule.

The type of spectroscopy involved will depend on the region of the electromagnetic spectrum that is used as a radiation source. In Infrared Spectroscopy, molecules absorb infrared radiation which brings about changes in stretching and bending motions of the molecule. The radiation absorbed is in the energy range with wavelengths (λ) between 2.5 and 17 μm (4000 cm-1 to 600 cm-1).

In Electronic (UV-visible) Spectroscopy, molecules absorb radiation in the UV-visible region (200 - 800 nm). This brings about electronic transitions within the molecule.

Since absorption of radiation is quantized (i.e. it is subject to certain quantum mechanical restrictions), only the allowed frequencies of radiation appear as absorption bands in the spectrum.

Vibrational Spectroscopy

All chemical bonds have a natural frequency of vibration (C-H, O-H, C=O, C-C, C=C) but the exact frequency will depend on their environment, i.e. on the actual structure of the molecule involved.

Identification of the vibrational frequencies indicates the different bonds present in a molecule and provides structural information about that molecule.

An infrared spectrum is a plot of % transmittance (y-axis) versus energy (cm-1) (x-axis) in the range 4000 cm-1 to 600 cm-1.

InfraredInfrared10,000 cm10,000 cm-1-1 to 100 cm to 100 cm-1-1

Converted in Vibrational energy in moleculesConverted in Vibrational energy in molecules

Vibrational Spectra appears as bands instead of sharp lines => as it is accompanied by a number of rotational changes

Wave Number => (cm-1) => proportional to energy

Depends on:•Relative masses of atoms•Force constant of bonds•Geometry of atoms

Older system uses the wavelenght (m => 10-6 m)

cm-1 = 104 / m

The Units:The Units:The frequency (s-1) => # vibrations per second

For molecular vibrations, this number is very large (1013 s-1) => inconvenient

More convenient : Wavenumber = c

(Frequency / Velocity)

e.g. = 3 * 10 = 3 * 101313 s s-1-1

= s

3 * 1010 cm s-1

= 1000 cm= 1000 cm-1-1

Wave Length : 1

=

Intensity:Intensity: Transmittance (TT) or %T%T

TT =II0

Absorbance (AA)

AA = log II0

Intensity in IRIntensity in IR

IRIR : Plot of %IR%IR that passes through a sample (transmittancetransmittance) vs WavelenghtWavelenght

InfraredInfrared

• Position, Intensity and Shape of bands gives clues on Structure of molecules

• Modern IR uses Michelson Interferometer=> involves computer, and Fourier Transform

SamplingSampling => plates, polished windows, Films …Must be transparent in IR

NaCl, KCl : Cheap, easy to polishNaCl, KCl : Cheap, easy to polish

NaClNaCl transparent to 4000 - 650 cm4000 - 650 cm-1-1

KClKCl transparent to 4000 - 500 cm4000 - 500 cm-1-1

KBr KBr transparent to 400 cm400 cm-1-1

Infrared: Low frequency spectra of Infrared: Low frequency spectra of window materialswindow materials

Bond length and strength Bond length and strength vs vs

Stretching frequencyStretching frequency

Bond C-H =C-H -C-H

Length 1.08 1.10 1.12

Strenght 506 kJ 444 kJ 422 kJ

IR freq. 3300 cm-1 3100 cm-1 2900 cm-1

IntroductionIntroduction

IR is one of the first technique inorganic chemists used (since 1940)

Molecular VibrationMolecular Vibration

Newton’s law of motion is used classically to calculate force constant

r

reFFFF The basic picture : atoms (mass) are

connected with bonding electrons. Re is the equilibrium distance and FF: force to restore equilibrium

F(x) = -kx where X is displacement from equilibrium

= = 11

22 √kkiiii

Where Where KKii is the force constant and is the force constant and ii is reduce mass of a particular motionis reduce mass of a particular motion

Because the energy is quantized: E = Because the energy is quantized: E = h h ii

IntroductionIntroduction

Displacement of atoms during vibration lead to distortion of Displacement of atoms during vibration lead to distortion of electrival charge distribution of the molecule which can be resolve electrival charge distribution of the molecule which can be resolve in dipole, quadrupole, octopole …. In various directionsin dipole, quadrupole, octopole …. In various directions

=> Molecular vibration lead to oscillation of electric charge => Molecular vibration lead to oscillation of electric charge governed by vibration frequencies of the systemgoverned by vibration frequencies of the system

Oscillating molecular dipole can interact directly with oscillating Oscillating molecular dipole can interact directly with oscillating electric vector of electromagnetic radiation of the same frequencyelectric vector of electromagnetic radiation of the same frequency

h h = = hh

Vibrations are in the range Vibrations are in the range 10101111 to 10 to 101313 Hz Hz => => 30 - 3,000 cm30 - 3,000 cm-1-1

Introduction: Symmetry selection ruleIntroduction: Symmetry selection rule

Stretching homonuclear diatomic molecule likeStretching homonuclear diatomic molecule like N N22 does not does not

generate oscillating dipolegenerate oscillating dipole Direct interaction with oscillating electronic Dipole is not possibleDirect interaction with oscillating electronic Dipole is not possible inactive in IRinactive in IR

There is no place here to treat fundamentals of symmetryThere is no place here to treat fundamentals of symmetryIn principle, the symmetry of a vibration need to be determinedIn principle, the symmetry of a vibration need to be determined

Calculating stretching frequenciesCalculating stretching frequenciesHooke’s law :Hooke’s law :

== 1122cc KK

: Frequency in cm: Frequency in cm-1-1

c : Velocity of light => 3 * 10c : Velocity of light => 3 * 101010 cm/s cm/s

K : Force constant => dynes /cmK : Force constant => dynes /cm

masses of atoms in gramsmasses of atoms in grams

mm11 m m22

mm11 + m + m22

MM11 M M22

MM11 + M + M22 (6.02 * 10 (6.02 * 102323))

== 4.124.12 KK

CC—C —C K = 5* 10K = 5* 1055 dynes/cm dynes/cm

CC=C =C K = 10* 10K = 10* 1055 dynes/cm dynes/cmCCC C K = 15* 10K = 15* 1055 dynes/cm dynes/cm

Calculating stretching frequenciesCalculating stretching frequencies

CC=C =C K = 10* 10K = 10* 1055 dynes/cm dynes/cm == 4.124.12 KK

MM11 M M22

MM11 + M + M22

(12)(12)(12)(12)12 + 1212 + 12

== 4.124.12 10* 1010* 1055

= 1682 cm= 1682 cm-1-1

Experimental Experimental 1650 cm 1650 cm-1-1

CC—H —H K = 5* 10K = 5* 1055 dynes/cm dynes/cm == 4.124.12 5* 105* 1055

= 3032 cm= 3032 cm-1-1

MM11 M M22

MM11 + M + M22

(12)(1)(12)(1)12 + 112 + 1


CC—D —D K = 5* 10K = 5* 1055 dynes/cm dynes/cm == 4.124.12 5* 105* 1055

= 2228 cm= 2228 cm-1-1

MM11 M M22

MM11 + M + M22

(12)(2)(12)(2)12 + 212 + 2


VibrationsVibrationswww.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm

Modes of vibrationModes of vibrationCC—H—HStretchingStretching

BendingBending CC

OO

HH

H

H

Symmetrical Symmetrical 2853 cm2853 cm-1-1

H

H

Asymmetrical Asymmetrical 2926 cm2926 cm-1-1

H

H

H

H

ScissoringScissoring1450 cm1450 cm-1-1

RockingRocking720 cm720 cm-1-1

HH

HH

WaggingWagging1350 cm1350 cm-1-1

TwistingTwisting1250 cm1250 cm-1-1

StretchingStretchingfrequencyfrequency

BendingBendingfrequencyfrequency

VibrationsVibrationswww.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm

General trends:General trends:•Stretching frequenciesStretching frequencies are higher than are higher than bending frequencies bending frequencies (it is easier to bend a bond than stretching or compresing them)(it is easier to bend a bond than stretching or compresing them)

•Bond involving Hydrogen are higher in freq. than with heavier atomsBond involving Hydrogen are higher in freq. than with heavier atoms

•Triple bondTriple bond have higher freq than have higher freq than double bonddouble bond which has higher freq which has higher freq than than single bondsingle bond

Structural Information from Vibration Structural Information from Vibration SpectraSpectra

• Spectrum can be treated as finger print to recognize Spectrum can be treated as finger print to recognize the product of a reaction as a known compound. the product of a reaction as a known compound. (require access to a file of standard spectra)(require access to a file of standard spectra)

• At another extreme , different bands observed can At another extreme , different bands observed can be used to deduce the symmetry of the molecule and be used to deduce the symmetry of the molecule and force constants corresponding to vibrations.force constants corresponding to vibrations.

• At intermediate levels, deductions may be drawn At intermediate levels, deductions may be drawn about the presence/absence of specific groupsabout the presence/absence of specific groups

The symmetry of a molecule determines the number of bands expectedThe symmetry of a molecule determines the number of bands expected

Number of bands can be used to decide on symmetry of a moleculeNumber of bands can be used to decide on symmetry of a molecule

Tha task of assignment is complicated by presence of low intensity bands and Tha task of assignment is complicated by presence of low intensity bands and presence of forbidden overtone and combination bands.presence of forbidden overtone and combination bands.There are different levels at which information from IR can be analyzed to There are different levels at which information from IR can be analyzed to allow identification of samples:allow identification of samples:

Methods of analyzing an IR spectrumMethods of analyzing an IR spectrum

The effect of The effect of isotopic substitutionisotopic substitution on the observed spectrum on the observed spectrumCan give valuable information about the atoms involved in a Can give valuable information about the atoms involved in a particular vibrationparticular vibration

1.1. Comparison with standard spectra : traditional approachComparison with standard spectra : traditional approach

2.2. Detection and Identification of impuritiesDetection and Identification of impuritiesif the compound have been characterized before, any bands that are not found in the pure sample can be assigned to the impurity (provided that the 2 spectrum are recorded with identical conditions: Phase, Temperature, Concentration)

3.3. Quantitative Analysis of mixtureQuantitative Analysis of mixtureTransmittance spectra = I/I0 x 100 => peak height is not lineraly related to intensity of absorptionIn Absorbance A=ln (Io/I) => Direct measure of intensity

Analyzing an IR spectrumAnalyzing an IR spectrum

In practice, there are similarities between frequencies of molecules In practice, there are similarities between frequencies of molecules containing similar groups.containing similar groups.

Group - frequency correlationsGroup - frequency correlations have been extensively developed for have been extensively developed for organic compounds and some have also been developed for organic compounds and some have also been developed for inorganicsinorganics

Some characteristic infrared absorption frequencies BOND COMPOUND TYPE FREQUENCY RANGE, cm-1

C-H alkanes 2850-2960 and 1350-1470

alkenes 3020-3080 (m) and

RCH=CH2 910-920 and 990-1000

R2C=CH2 880-900

cis-RCH=CHR 675-730 (v)

trans-RCH=CHR 965-975

aromatic rings 3000-3100 (m) and

monosubst. 690-710 and 730-770

ortho-disubst. 735-770

meta-disubst. 690-710 and 750-810 (m)

para-disubst. 810-840 (m)

alkynes 3300 O-H alcohols or phenols 3200-3640 (b) C=C alkenes 1640-1680 (v)

aromatic rings 1500 and 1600 (v) C≡C alkynes 2100-2260 (v) C-O primary alcohols 1050 (b)

secondary alcohols 1100 (b)

tertiary alcohols 1150 (b)

phenols 1230 (b)

alkyl ethers 1060-1150

aryl ethers 1200-1275(b) and 1020-1075 (m) all abs. strong unless marked: m, moderate; v, variable; b, broad

• IR spectra of ALKANES• C—H bond “saturated”• (sp3) 2850-2960 cm-1• + 1350-1470 cm-1

• -CH2- + 1430-1470• -CH3 + “ and 1375 • -CH(CH3)2 + “ and 1370, 1385• -C(CH3)3 + “ and 1370(s), 1395 (m)

n-pentane

CH3CH2CH2CH2CH3

3000 cm-1

1470 &1375 cm-1

2850-2960 cm-1

sat’d C-H

n-pentane

CH3CH2CH2CH2CH3

3000 cm-1

1470 &1375 cm-1

2850-2960 cm-1

sat’d C-H

CH3CH2CH2CH2CH2CH3

n-hexane

2-methylbutane (isopentane)

2,3-dimethylbutane

IR of ALKENES

=C—H bond, “unsaturated” vinyl

(sp2) 3020-3080 cm-1

+ 675-1000

RCH=CH2 + 910-920 & 990-1000

R2C=CH2 + 880-900

cis-RCH=CHR + 675-730 (v)

trans-RCH=CHR + 965-975

C=C bond 1640-1680 cm-1 (v)

1-decene

910-920 & 990-1000 RCH=CH2

C=C 1640-1680

unsat’dC-H

3020-3080 cm-1

4-methyl-1-pentene

910-920 & 990-1000 RCH=CH2

2-methyl-1-butene

IR spectra BENZENEs

=C—H bond, “unsaturated” “aryl”

(sp2) 3000-3100 cm-1

+ 690-840

mono-substituted + 690-710, 730-770

ortho-disubstituted + 735-770

meta-disubstituted + 690-710, 750-810(m)

para-disubstituted + 810-840(m)

C=C bond 1500, 1600 cm-1

ethylbenzene

690-710, 730-770 mono-

1500 & 1600

Benzene ring

3000-3100 cm-1

Unsat’d C-H

IR spectra ALCOHOLS & ETHERS

C—O bond 1050-1275 (b) cm-1

1o ROH 1050

2o ROH 1100

3o ROH 1150

ethers 1060-1150

O—H bond 3200-3640 (b)

1-butanol

CH3CH2CH2CH2-OH

C-O 1o

3200-3640 (b) O-H

2-butanol

C-O 2o

O-H

HydrogeHydrogen bond n bond

and C=Oand C=O

Intensity of C=O vs C=CIntensity of C=O vs C=C

Band Shape: OH vs NH2 vs Band Shape: OH vs NH2 vs CHCH

Free OH and Hydrogen bonded OHFree OH and Hydrogen bonded OH

Symmetrical and asymmetrical stretch Symmetrical and asymmetrical stretch

MethylMethyl 2872 cm2872 cm-1-1

Symmetrical StretchSymmetrical Stretch Asymmetrical StretchAsymmetrical Stretch

——CC——HH

HH

HH

——CC——HH

HH

HH

AnhydrideAnhydrideOO

OO OO1760 cm1760 cm-1-1

2962 cm2962 cm-1-1

1800 cm1800 cm-1-1

OO

OO OO

AminoAmino

NitroNitro

——NNHH

HH3300 cm3300 cm-1-1

3400 cm3400 cm-1-1

1350 cm1350 cm-1-1 1550 cm1550 cm-1-1

——NNHH

HH

——NN

OO

OO——NN

OO

OO

General IR commentsGeneral IR commentsPrecise treatment of vibrations in molecule is not feasible herePrecise treatment of vibrations in molecule is not feasible hereSome information from IR is also contained in MS and NMRSome information from IR is also contained in MS and NMR

Certain bands occur in Certain bands occur in narrow regionsnarrow regions : : OHOH, , CHCH, , C=OC=O

Detail of the structure is revealed by the Detail of the structure is revealed by the exact positionexact position of the band of the band

e.g. e.g. KetonesKetonesO

1715 cm1715 cm-1-1

CH

O

CH2

1680 cm1680 cm-1-1

Region 4000 – 1300 : Functional groupRegion 4000 – 1300 : Functional group

Absence of band in this region can be used to deduce absence of groupsAbsence of band in this region can be used to deduce absence of groupsCaution: some bands can be very broad because of hydrogen bonding Caution: some bands can be very broad because of hydrogen bonding

e.g. e.g. Enols v.broad OH, C=O absent!!Enols v.broad OH, C=O absent!!

Weak bands in high frequency are extremely useful : S-H, CWeak bands in high frequency are extremely useful : S-H, CC, CC, CNN

Lack of strong bands in 900-650 means no aromaticLack of strong bands in 900-650 means no aromatic

AlkanesAlkanes, , AlkenesAlkenes, , AlkynesAlkynes

C-H : C-H : <3000 cm<3000 cm-1-1 >3000 cm>3000 cm-1-1 3300 cm3300 cm-1-1 sharpsharp

C-CC-C

StretchStretch

Not usefulNot useful

C=CC=C

CCCC

1660-1600 cm1660-1600 cm-1-1

conj. Moves to lower valuesconj. Moves to lower values Symmetrical : no bandSymmetrical : no band

2150 cm2150 cm-1-1

conj. Moves to lower valuesconj. Moves to lower valuesWeak but very usefulWeak but very useful

Symmetrical no bandSymmetrical no band

BendingBending CHCH2 2 RockingRocking

720 cm720 cm-1 -1 indicateindicatePresence of 4-CHPresence of 4-CH2 2

1000-700 cm1000-700 cm-1-1 Indicate substitutionIndicate substitution

patternpattern

C-H ~630 cmC-H ~630 cm-1-1 Strong and broadStrong and broad

Confirm triple bondConfirm triple bond

AlkaneAlkane

Alkene : Alkene : 1-Decene1-Decene

To give rise to absorption of IRTo give rise to absorption of IR => Oscillating Electric DipoleOscillating Electric DipoleSymmetrySymmetry

Molecules with Center of symmetryMolecules with Center of symmetrySymmetric vibration => inactiveSymmetric vibration => inactiveAntisymmetric vibration => activeAntisymmetric vibration => active

AlkeneAlkene

In large molecule local symmetry produce In large molecule local symmetry produce weak or absent vibrationweak or absent vibration

C=CC=CRR

RRtranstrans C=C isomer -> weak in IR C=C isomer -> weak in IR

Observable in RamanObservable in Raman

Alkene: Factors influencing vibration frequencyAlkene: Factors influencing vibration frequency

1- Strain move peak to right (decrease )1- Strain move peak to right (decrease )CCCC

CC

angleangle

16501650 16461646 16111611 156615661656 : exception1656 : exception

2- Substitution increase2- Substitution increase

3- conjugation decrease3- conjugation decrease C=C-Ph 1625 cmC=C-Ph 1625 cm-1-1

15661566 16411641 16751675

16111611 16501650 16791679

16461646 16751675 16811681

Alkene: Out-of-Plane bending Alkene: Out-of-Plane bending

This region can be used to deduce substitution patternThis region can be used to deduce substitution pattern

Alkyne: Alkyne: 1-Hexyne1-Hexyne

Alkyne:Alkyne:SymmetrySymmetry

In IR, Most important transition involve :In IR, Most important transition involve :

Ground State (Ground State (i i = 0) = 0) to to First Excited State (First Excited State (i = 1)i = 1)

TransitionTransition ((i i = 0) = 0) to to ((JJ = 2) = 2) => Overtone => Overtone

IR : AromaticIR : Aromatic

=C-H=C-H > 3000 cm> 3000 cm-1-1

C=CC=C 1600 and 1475 cm1600 and 1475 cm-1-1

=C-H=C-H out of plane bending: great utility to assign ring substitutionout of plane bending: great utility to assign ring substitution

overtoneovertone 2000-1667: useful to assign ring substitution2000-1667: useful to assign ring substitution

e.g. Naphthalene: e.g. Naphthalene: Substitution patternSubstitution pattern Isolated HIsolated H 862-835862-835

835-805835-805

760-735760-735

2 adjacent H2 adjacent H

4 adjacent H4 adjacent H

out of plane bendingout of plane bending

Aromatic substitution: Out of plane Aromatic substitution: Out of plane bendingbending

Aromatic substitution: Out of plane Aromatic substitution: Out of plane bendingbending

Aromatic and Alkene substitutionAromatic and Alkene substitution

IR: Alcohols and PhenolsIR: Alcohols and Phenols

O-H Free : Sharp 3650-3600O-H Free : Sharp 3650-3600

O-H H-Bond : Broad 3400-3300O-H H-Bond : Broad 3400-3300

Intermolecular Hydrogen bonding Increases with concentration=> Less “Free” OHLess “Free” OH

IR: Alcohols and PhenolsIR: Alcohols and Phenols

C-O : 1260-1000 cmC-O : 1260-1000 cm-1-1 (coupled to C-C => C-C-O) (coupled to C-C => C-C-O)

C-O Vibration is sensitive to substitution:C-O Vibration is sensitive to substitution:

PhenolPhenol 122012203` Alcohols3` Alcohols 115011502` Alcohols2` Alcohols 110011001` Alcohols1` Alcohols 10501050

More complicated than above: shift to lower Wavenumber More complicated than above: shift to lower Wavenumber With unsaturation (Table 3.2)With unsaturation (Table 3.2)

AlcoholAlcohol

C-O : 1040 cmC-O : 1040 cm-1 -1 indicate primary alcohol indicate primary alcohol

Benzyl AlcoholBenzyl Alcohol

OHOH spsp22spsp33

PhPhovertoneovertone

C-O : 1080, 1022 cmC-O : 1080, 1022 cm-1 -1 : primary OH: primary OH

MonoMonoSubst. PhSubst. Ph735 & 697 cm735 & 697 cm-1-1

PhenolPhenol

OHOH spsp22


C=C stretchC=C stretch

Ph-O : 1224 cmPh-O : 1224 cm-1-1

MonoMonoSubst. PhSubst. Phout-of planeout-of plane810 & 752 cm810 & 752 cm-1-1

PhenolPhenol

IR: EtherIR: EtherC-O-CC-O-C =>=> 1300-1000 cm1300-1000 cm-1-1

Ph-O-C Ph-O-C =>=> 1250 and 1040 cm1250 and 1040 cm-1-1

AliphaticAliphatic => => 1120 cm1120 cm-1-1

C=C in vinyl Ether C=C in vinyl Ether => => 1660-1610 cm1660-1610 cm-1-1

appear as Doublet => rotational isomersappear as Doublet => rotational isomers

CH2 CH

O CH3

~1620~1620

~1640~1640

H2C CH

O CH3

H2C CH

O

CH3

EtherEther

spsp22

spsp33


C=C stretchC=C stretch

Ph-O-C : 1247 cmPh-O-C : 1247 cm-1-1 Asymmetric stretch Asymmetric stretchPh-O-C : 1040 cmPh-O-C : 1040 cm-1-1 Symmetric stretch Symmetric stretch

MonoMonoSubst. PhSubst. Phout-of planeout-of plane784, 754 & 692 cm784, 754 & 692 cm-1-1

O

H

CH

CH3

CH3

CH3

O

IR: CarbonylIR: Carbonyl From 1850 – 1650 cmFrom 1850 – 1650 cm-1-1

Ketone 1715 cmKetone 1715 cm-1-1 is used as reference point for comparisons is used as reference point for comparisons

1715 1715 16901690 1725 1725 1700 1700 1710 1710 16801680

18101810AnhydrAnhydrBandBand

18001800AcidAcid

ChlorideChloride

17601760AnhydrAnhydrBand 2Band 2

17351735EsterEster

17251725AldehydeAldehyde

17151715KetoneKetone

17101710AcidAcid

16901690AmideAmide

Factor influencing Factor influencing C=OC=O

1) conjugation1) conjugationC=CC=C

CC

OO

CC++——CCCC

OO--

Conjugation increase single bond character of Conjugation increase single bond character of C=OC=O Lower force constantLower force constant lower frequency numberlower frequency number

O

OH

Ketone and ConjugationKetone and ConjugationConjugation: LowerConjugation: Lower

Ketone and Ring StrainKetone and Ring Strain

Ring Strain: HigherRing Strain: Higher

Factors influencing Factors influencing C=OC=O

2) Ring size2) Ring size

O

1715 cm1715 cm-1-1

Angle ~ 120Angle ~ 120oo

CH3

CH3

O

O

1751 cm1751 cm-1-1

< 120< 120oo

O

1775 cm1775 cm-1-1

<< 120<< 120oo

Factors influencing carbonyl: Factors influencing carbonyl: C=OC=O

3) 3) substitution effect (Chlorine or other halogens) substitution effect (Chlorine or other halogens)

——CC——CC——

XX

OO

Result in stronger bound Result in stronger bound higher frequency higher frequency O

Cl 1750 cm1750 cm-1-1

4) Hydrogen bonding 4) Hydrogen bonding Decrease Decrease C=OC=O strenght strenghtlower frequencylower frequency

O

OCH3

OH

1680 cm1680 cm-1-1

EnolEnol

Factors influencing carbonyl: Factors influencing carbonyl: C=OC=O5) Heteroatom5) Heteroatom

Y

R

O

Inductive effectInductive effect

Stronger bondStronger bondhigher frequencyhigher frequency

e.g. estere.g. ester

Y

R

O

Resonance effectResonance effectWeaker bondWeaker bondLower frequence Lower frequence

e.g. amidese.g. amides

YY C=OC=O

ClCl

BrBr

OH (monomer)OH (monomer)

OR (Ester)OR (Ester)

1815-17851815-1785

18121812

17601760

1705-17351705-1735

NH2NH2

SRSR

1695-16501695-1650

1720-16901720-1690

inductiveinductive

resonanceresonance

Ester CarbonylEster Carbonyl

EstersEsters C=O C=O ~ 1750 – 1735 cm~ 1750 – 1735 cm-1-1

O-C : 1300 – 1000 2 or more bandsO-C : 1300 – 1000 2 or more bands

Conjugation => lower freq.

R OR

O

Inductive effect with OInductive effect with O reinforce carbonyl => higherhigher

Conjugation withConjugation with CO CO weaken carbonyl => LowerLower

Ester carbonyl: Ester carbonyl: C=OC=O


C=O : 1765 cmC=O : 1765 cm-1-1 C-O 1215 cmC-O 1215 cm-1-1

1193 cm1193 cm-1-1

spsp22

C=OC=O


Ester carbonyl : effect of conjugationEster carbonyl : effect of conjugation

Lactone carbonyl: Lactone carbonyl: C=OC=O

Lactones Lactones Cyclic Ester Cyclic Ester

O

O

1735173517201720 17601760

1770177017501750 18001800

O

O

O

O

OO

OO O

O

Carbonyl compounds : AcidsCarbonyl compounds : Acids

Carboxylic acidCarboxylic acid

Exist as dimer :Exist as dimer :CH3 C

OH

O

CH3C

OH

O

Strong Hydrogen bondStrong Hydrogen bond

OH : Very broad OH : Very broad 3400 – 2400 cm 3400 – 2400 cm-1-1

C=O : broad C=O : broad 1730 – 1700 cm 1730 – 1700 cm-1-1

CC——O : 1320 – 1210 cmO : 1320 – 1210 cm-1-1 Medium intensity Medium intensity

Carbonyl compounds : AcidsCarbonyl compounds : Acids

C=OC=O

OHOH

C=O : 1711 cmC=O : 1711 cm-1-1

OH : Very Broad 3300 to 2500 cmOH : Very Broad 3300 to 2500 cm-1-1 C-O : 1285, 1207 cmC-O : 1285, 1207 cm-1-1

AnhydridesAnhydrides

CH3 O

O

CH3

O C=O always has 2 bands:C=O always has 2 bands:

1830-1800 and 1775-1740 cm1830-1800 and 1775-1740 cm-1-1

CC—O multiple bands 1300 – 900 cm—O multiple bands 1300 – 900 cm-1-1

Carbonyl compounds : AldehydesCarbonyl compounds : AldehydesAldehydesAldehydes C=O C=O ~ 1725 cm~ 1725 cm-1-1

O=C-H : 2 weak bands 2750, 2850 cmO=C-H : 2 weak bands 2750, 2850 cm-1-1

Conjugation => lower freq.

C=O : 1724 cmC=O : 1724 cm-1-1

Carbonyl compounds : AldehydesCarbonyl compounds : Aldehydes

AldehydesAldehydes

Other carbonylOther carbonylAmidesAmides

LactamsLactams

Acid ChloridesAcid Chlorides

C=O ~1680-1630 cmC=O ~1680-1630 cm-1 -1 (band I)(band I)

NHNH22 ~ 3350 and 3180 cm ~ 3350 and 3180 cm-1-1 (stretch) (stretch)

NH ~ 3300 cmNH ~ 3300 cm-1-1 (stretch) (stretch)

NH ~ 1640-1550 cmNH ~ 1640-1550 cm-1-1 (bending) (bending)

NH

O

RR——C C —— ClCl

OO

1810-1775 cm1810-1775 cm-1-1

C C —— Cl 730 – 550 cm Cl 730 – 550 cm-1-1

~1660~1660

NH

O

~1705~1705

NH

O

~1745~1745

Increase with strainIncrease with strain

AmidesAmides

NHNH22 : Symmetrical stretch =>3170 cm : Symmetrical stretch =>3170 cm-1-1

asymmetrical stretch => 3352 cmasymmetrical stretch => 3352 cm-1-1

C=O : 1640 cmC=O : 1640 cm-1-1

NH Out of planeNH Out of plane

AmidesAmides

Acid ChloridesAcid Chlorides

Amino acidAmino acid

Exist as zwitterions Exist as zwitterions

CCCOCO22

--

NHNH33++

NHNH33++ : very broad 3330-2380 : very broad 3330-2380

(OH + (OH + NHNH33++ ))

CC

OO

OO1600 – 1590 strong1600 – 1590 strong

Amino acidAmino acid

AmineAmine

NH 3500 – 3300 cmNH 3500 – 3300 cm-1-1 NH : 2 bandsNH : 2 bandsNH : 1 bandNH : 1 band

NH bending : 1650 – 1500 cmNH bending : 1650 – 1500 cm-1-1

C-N : 1350 – 1000 cmC-N : 1350 – 1000 cm-1-1

NH out-of-plane : ~ 800 cmNH out-of-plane : ~ 800 cm-1-1

Amine saltAmine salt

NHNH++ 3500 – 3030 cm 3500 – 3030 cm-1-1 broad / strong broad / strong

Ammonium Ammonium primary primary secomdary secomdary

rightright

LeftLeft

AmineAmine

Primary AminePrimary Amine

Secondary AmineSecondary Amine

Tertiary AmineTertiary Amine

Aromatic AmineAromatic Amine

Other Nitrogen CompoundsOther Nitrogen Compounds

NitrilesNitriles

IsocyanatesIsocyanates

IsothiocyanatesIsothiocyanates

Imines / OximesImines / Oximes

R-CR-CN : N : Sharp 2250 cmSharp 2250 cm-1-1

Conjugation moves to lower frequencyConjugation moves to lower frequency

R-N=C=OR-N=C=O Broad ~ 2270 cmBroad ~ 2270 cm-1-1

R-N=C=SR-N=C=S 2 Broad peaks ~ 2125 cm2 Broad peaks ~ 2125 cm-1-1

R R 22C=N-RC=N-R 1690 - 1640 cm1690 - 1640 cm-1-1

NitrileNitrile C N

CH3

NitrileNitrile

Nitrile and IsocyanateNitrile and Isocyanate

NitroNitro

——NNOO

OO

++--

Aliphatic :Aliphatic : Asymmetric : 1600-1530 cmAsymmetric : 1600-1530 cm-1-1

Symmetric : 1390-1300 cmSymmetric : 1390-1300 cm-1-1

Aromatic :Aromatic : Asymmetric : 1550-1490 cmAsymmetric : 1550-1490 cm-1-1

Symmetric : 1355-1315 cmSymmetric : 1355-1315 cm-1-1

NitroNitro

NitroNitro

SulfurSulfur

MercaptansMercaptans S – H : weak 2600-2550 cmS – H : weak 2600-2550 cm-1-1

Since only few absorption in that range it confirm its presenceSince only few absorption in that range it confirm its presence

Sulfides,Disulfides : no useful informationSulfides,Disulfides : no useful information

Sulfoxides:Sulfoxides:

RS

R

O Strong ~ 1050 cmStrong ~ 1050 cm-1-1

SulfonesSulfones:: Asymetrical ~ 1300 cmAsymetrical ~ 1300 cm-1-1

Symetrical ~ 1150 cmSymetrical ~ 1150 cm-1-1 R S R

O

O

2 bands :2 bands :

Sulfur: Mercaptan R-Sulfur: Mercaptan R-S-HS-H

Sulfur: Sulfonyl ChlorideSulfur: Sulfonyl Chloride

S=O : S=O : Asymmetrical stretch: 1375 cm-1Asymmetrical stretch: 1375 cm-1Symmetrical Stretch : 1185 cm-1Symmetrical Stretch : 1185 cm-1

Sulfur: SulfonateSulfur: Sulfonate


S-O : several bands between 1000 – 750 cmS-O : several bands between 1000 – 750 cm-1-1

Sulfur: SulfonamideSulfur: Sulfonamide


NHNH22 stretch: 3350 and 3250 cm stretch: 3350 and 3250 cm-1-1 NH Bend: 1550 cmNH Bend: 1550 cm-1-1

HalogensHalogens

CC—F : 1400 – 1000 cm—F : 1400 – 1000 cm-1-1

CC—Cl : strong 785 – 540 cm—Cl : strong 785 – 540 cm-1-1

CC—Br : 650 – 510 cm—Br : 650 – 510 cm-1-1 (out of range with NaCl plates) (out of range with NaCl plates)

CC—I : 600 – 485 cm—I : 600 – 485 cm-1-1 (out of range) (out of range)

HalogensHalogens

PhosphorusPhosphorus

Phosphines: R-PHPhosphines: R-PH2 2 R R22PHPH

PP—H : Sharp 2320 – 2270 cm—H : Sharp 2320 – 2270 cm-1-1

PPHH22 bending : 1090 – 1075 and 840 - 810 cm bending : 1090 – 1075 and 840 - 810 cm-1-1

PPH bending : 990 - 886 cmH bending : 990 - 886 cm-1-1

Phosphine Oxide : RPhosphine Oxide : R33 P=O P=O

PP=O very strong : 1210 - 1140 cm=O very strong : 1210 - 1140 cm-1-1

Phosphate Esters : (OR)Phosphate Esters : (OR)33 P=O P=O

PP=O very strong : 1300 - 1240 cm=O very strong : 1300 - 1240 cm-1-1

PP-O very strong : 1088 – 920 cm-O very strong : 1088 – 920 cm-1-1

PP-O : 845 - 725 cm-O : 845 - 725 cm-1-1

SiliconSilicon

IR-OrganometallicIR-OrganometallicIndex

Si-H :Si-H : 2200 cm2200 cm-1-1 (Stretch) (Stretch)

950 – 800 cm950 – 800 cm-1-1 (bend) (bend)

Si-O-H :Si-O-H : OH: 3700 – 3200 cmOH: 3700 – 3200 cm-1-1 (Stretch) (Stretch)

Si-O : 830 – 1110 cmSi-O : 830 – 1110 cm-1-1

Health & Medicine

Infrared presentation