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Premium member Presentation Transcript Slide 1: 1 A Presentation on factors affecting infrared spectroscopy Guided By:- Mr.Dharmendra Baria Lecturer Presented By:- Jinesh gandhi Roll No. 08 email@example.com Department of QA DDPCSlide 2: 2 Contents:- Vibrational coupling Requirment for vibration Fermiresonance Hydrogen bonding Electronic effect Resonance effect Inductive effect Bond angle Interaction b/w solute & solvent Concentration of analyte Nature of solvent Temperature effectSlide 3: 3 Factors influencing vibrational frequency:- (1) Vibrational coupling:- Here, interaction of 2 vibrational level which vibrate at same frequency and near by in molecule known as vibrational coupling Occur only when bonds are located closely to each other. Here,2 more peaks appear in spectra. (1)symmetric (2)AntisymetricSlide 4: 4 Requirements:- 2 Stretching vibrational coupling occur when it is separated through common atom. 2 bending vibrational coupling occur when it is separated by common bond. Coupling can occur between stretching and banding if bond involved in stretching is involved in bending also. Both vibrator should vibrate with same frequency.Slide 5: 5 If no.of bonds will increase or seperated by more than 2 atoms vibrational coupling is negligible. E.g;-(1)-C-H show streching vibration only. -C - H appear 2 peaks H Antisymmetric:-at 3000cm-1 Symmetric :-at 2900cm-1Slide 6: 6 If H - C - H here,antisymmetric:-at 3100cm-1 H symmetric:-at 3000cm-1 (2) CO 2 it is linear molecule so no. of peaks should be 3n-5 = 3*3-5= 4 But here only 2 peaks appear in spectra that is anti-symmetric and bending. Antisymmetric peak appear at 2350cm- Here in symmetric peak doesn’t appear because of there is no change in dipole moment -Therefore it is IR inactive And instead of 2 bending peaks only one bending peak appear because energy of absorption is same.Slide 7: 7 (3) Acetaldehyde (CH3-CH0) Here n=7 and molecule is non linear so no. of vibrational peaks should be 15 according to 3n-6 But here only 5 peaks appear in spectra (4) H 2 O Here 3 peaks appear according to 3n-6 Symmetric peak appear at 3650 cm-1 Antisymmetric peak at 3760 cm-1 Bending peak at 1595 cm-1Slide 8: 8 (5) Anhydride:- R-C-O-C-R O O These give rise to 2-C=Ostr absorption,1 antisymmetric and 1 symmetric peak. Here,coupling between 2 carbonyl groups which are indirectly linked through –O-. (6) Amide R-CONH 2 Shows 2 absorption bands around 1600-1700cm-1 i.e. due to –C=O str and –N-H def.Slide 9: 9 but due to coupling original character is changed. Here coupling between –C-N stretching and –N-H bending vibrational level takes place Here amide I peak due to –C=O stretching and amide II peak due to coupling.Slide 10: 10 Fermiresonance:- interaction between fundamental vibrations and overtones known as Fermiresonance. E.g (1) aldehyde(R-CHO):- Here coupling between –C-H stretch and overtone of –C-H str occurSlide 11: 11 (2)Inorganic structure :- appearance of doublet of –C=O stretch of cyclopentanone ,Fermiresonance with an overtone or combination band of an alfa-methylene group shows 2 absorption in the carbonyl stretch regionSlide 12: 12 (2) Hydrogen bonding:- Possible only if any system contain 1 proton donor and 1 proton acceptor groups in system. Here,”s” orbital of proton donor overlaps ”p” or “ ”orbital of proton acceptor group. E.g of donors:--COOH -OH -NH2 -CONH2 E.g: of acceptor:- any system containing “=“ H bonding is denoted by “-----”Slide 13: 13 2 types of H-bonding (1) inter molecular (2) intra molecular H-bond occur at how much extent depends on geometry, nature of proton donor/acceptor ,ring strain existing in molecule. At low concentration 2 peaks appear for alcohol. -the sharp band is of –O-H str in free alcohol -the broad band is due to H-bonded –O-H strSlide 14: 14 E.g:- in which intermolecular H-bonding occur alcohol, phenol,carboxylic acid,etc. E.g:- in which intramolecular H-bonding occur o-chloro and o-alkoxy phenols,beta-hydroxy amino/nitro compoundsSlide 15: 15 but due to coupling original character is changed. Here coupling between –C-N stretching and –N-H bending vibrational level takes place Here amide I peak due to –C=O stretching and amide II peak due to coupling.Slide 16: 16 Hydrogen bonding is strongest when bonded structure is stabilized by resonance. E.g:- (1) salicylic acid (o-hydroxy benzoic acid/p-hydroxy benzoic acid):- here, both shows different peaks because OHBA shows intramolecular H-bond (2) phenol:- shows inter/intramolecular H-bondingSlide 17: 17 (3) Enols/chelates:- here, H-bonding is so strong that even though diluting solution it can’t break -C- and –OH:-here, H-bond with O of –C=O so, decreased double bond characteristic. Depends on basicity of –C=O group. If more basic stronger H bond. -COOH also shows H-bondingSlide 18: 18 (4) Aromatic compounds posses pie-system:- -so. posses conjugation. -act as Lewis base. -so. decreased ‘=‘characteristic -so, deceased F (5) -NH 2 :- shows 2 peaks, at 3000cm-1 and 3600cm-1 -if free amino group shows peak at 3600cm-1 -if H-bonded amino group shows peak at 3000cm-1 - H-bond in –N-H is more weaker than that of in –OH.Slide 19: 19 ( 3)Electronic effects:- depends on presence of substituent. (a)conjugation:- cause delocalization of electron, -so, decreases “=“c increases bond lenth decreases bond strength so decrease on vibrational frequency.Slide 20: 20 0-here, delocalization of -electron between –C=O and ring increases double bond character of bond joining them.Slide 21: 21 (b)Resonance effect(mesomeric effect):- means single molecule can be represented in 2 or more than 2 forms -if electron releasing group present increases in delocalization decreases in “=“ characteristic increases in bond length decreases bond strength so, decreases vibrational frequency.Slide 22: 22 (c)Inductive effect:- -Inductive and resonance both type of effects are existing in molecule. -finally which type of effect is shown by molecule depends on which effect is predominant. E.g:- Amides:- (1)R-C-NH2:- NH2 is electronreleasing group so, more resonance effect so decreases F so, decreases vibrational frequencySlide 23: 23 (2)R-CO-Cl:- -C=O is electron withdrawing O group so,decreases in delocalization of electron so, increases bond strength so, increases in vibrational frequency (3)Esters:- R-C-0O-R1:-if alkyl esters resonance effect is predominant If R=benzene inductive effect is predominant.Slide 24: 24 (4)Field effect:- If 2 functional group present and 1 affect the vibration of other known as field effect. OCH3 C=O:- here, Cl- present in equatorial position 2 functional groups are near each other so, repulsion occur When –C=O group is in axial position no field effectSlide 25: 25 (5)Bond angle:- Normal bond angle is of 120. -if decrease in angle strain occur bond length is decreased and “=“characteristic is increased. increased F increadsed vibrational frequency. If ring expands increased length of bond so decreased F so, decreased vibrational frequencySlide 26: 26 6)Interaction between solute and solvent:- Due to this change in position and shape of IR peak. 7) Concentration of analyte :- Increased concentration of analyte so, more interaction so, band broadeningSlide 27: 27 (9)Temperature effect:- If increased temperature increased interaction so band broadening also, there may be change in position and shape of IR spectraSlide 28: 28 References:- 1) Instrumental analysis By skoog;hooler;crouch India edition reprint 2008; page No.486-7 2) Handbook instru.techniques for analytical techniques By frank settle India reprint 2004;page No.251-2 3)Organic spectroscopy,william kemp,3 rd edition 4)Spectrometic identification of organic compound,Robert M.silverstein,francis X.webster,6 th edition 5)Introduction to instrumental analysis,Robert D.BrounSlide 29: 29 Frequently asked question in exam:- Explain the principle of IR. Discuss factor affecting tbe carbonyl streching in IR spectroscopy.Slide 30: 30 Thank you You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.