WOODWARD-FIESER RULE WITH Eg. DERIVATIVE SPECTROSCOPY

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Presentation Transcript

DERIVATIVE SPECTROSCOPY : 

DERIVATIVE SPECTROSCOPY Spectra are obtained by plotting the first or a higher- order dervitave of absorbance w.r.t. Wavelenght Concentration measurements of an analyte in presense of an interference or of two or more analyte can be made more easily and accurately using derivative spectrum

It should be noted that taking a derivative enhances noise, so high quality spectra are a must for using this technique : 

It should be noted that taking a derivative enhances noise, so high quality spectra are a must for using this technique Application of derivative spectra Quantitative identification of species The enhanced detail of a derivative spectra makes it possible to distinguish among compounds having overlapping spectra, a technique often called feature enhancement

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used to determine trace metals in mixtuers eg: Trace amount of Mn and Zn can be determined in mixtures by forming complex with 5,8-dihydroxy 1,4-naphthaquinone Also in pharmaceutical preparations ,vitamine mixtures

WOODWARD-FEISER RULE : 

WOODWARD-FEISER RULE Woodward (1941) : gave certain rules for correlating max with molecular structure Scott-Feiser (1959): modified rule with more experimental data, the modified rule is known as Woodward-Feiser rule used to calculate the position of max for a given structure by relating the position and degree of substitution of chromophore.

Homoannular diene: cyclic diene having conjugated double bonds in the same ring. : 

Homoannular diene: cyclic diene having conjugated double bonds in the same ring. Heteroannular diene: cyclic diene having conjugated double bonds in different ring

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2. Endocyclic double bond: double bond present in a ring 3. Exocyclic double bond: double bond in which one of the doubly bonded atoms is a part of a ring system Ring A Ring B Ring A has one exocyclic and endocyclic double bond. Ring B has only one endocyclic double bond

Woodward-Feiser rule for conjugated dienes, triens, polyenes : 

Woodward-Feiser rule for conjugated dienes, triens, polyenes Each type of diene or triene system is having a certain fixed value at which absorption takes place; this constitutes the BASIC VALUE or PARENT VALUE The contribution made by various alkyl substituents or ring residue,double bonds extending conjugation and polar groups such as –Cl, -Br are added to the basic value to obtain max for a particular compound

Parent values and incriments for different substituent/groups : 

Parent values and incriments for different substituent/groups Parent value Acyclic conjugated diene and : 215nm heteroannular conjugated diene Homoannular conjugated diene : 253nm Acyclic triene : 245nm

Increments : 

Increments Each alkyl substituents or ring residue : 5 nm Exocyclic double bond : 5 nm Double bonds extending conjugation : 30nm Auxochrome : -OR : 6 nm -SR : 30 nm -Cl, -Br : 5 nm -NR2 : 60nm -OCOCH3 : 0 nm

Calculate max for 1,4- dimethylcyclohex-1,3-diene : 

Calculate max for 1,4- dimethylcyclohex-1,3-diene H3C CH3 H3C CH3 Parent value for homoannular ring : 253 nm Two alkyl substituents : 2 * 5= 10 nm Two ring residue : 2 * 5= 10 nm calculated value : =273 nm observed value : = 263 nm

Calculate max : 

Calculate max Parent value for heteroannular diene : 215 nm Four ring residue : 4 * 5 = 20 nm calculated value : 235 nm observed value : 236 nm

Calculate max : 

Calculate max Parent value for heteroannular diene : = 215 nm Three ring residue : 3 * 5 = 15 nm One exocyclic double bond : = 5 nm Calculated value : = 235 nm Observed value : = 235 nm

Woodward-Feiser Rules for ,-unsaturated carbonyl compounds : 

Woodward-Feiser Rules for ,-unsaturated carbonyl compounds Parent values ,-unsaturated acyclic or six membered ring : 215 nm ketone ,-unsaturated five – membered ring ketone : 202nm ,-unsaturated aldehyde : 207 nm Increments Each alkyl substituent or ring residue at  position : 10 nm at  position : 12 nm at  position : 18 nm

Each exocyclic double bond : 5 nm : 

Each exocyclic double bond : 5 nm Double bond extending conjugation : 30 nm Homoannular conjugated diene : 39 nm Auxochromes position

Calculate max CH3-C(O)-C(CH3)=CH2 : 

Calculate max CH3-C(O)-C(CH3)=CH2 O CH3-C-C= CH2 CH3 Parent value for ,-unsaturated acyclic : 215 nm ketone one alkyl substituent in  position : 10 nm calculated value = 225 nm observed value = 220 nm

CALCULATE max : 

CALCULATE max Parent value for ,-unsaturated 6 : 215 nm membered cyclic ketone One ring residue at  position : 10nm Two ring residue at  position : 2* 12 = 24 nm Double bond exocyclic to two ring : 2* 5 = 10nm calculated value : 259nm observed value : 256nm

CALCULATE max β α : 

CALCULATE max β α Parent value : 215 nm One α ring residue : 10nm One δ residue : 18nm One double bond extending : 30nm conjugation One homoannular conjugated diene : 39nm One exocyclic double bond : 5nm Calculated value : = 317nm Observed value : = 319nm

CALCULATE max : 

CALCULATE max CH3 C=CH-C-CH3 CH3 C-CH=CH-CH3 CH3 Parent ,-unsaturated acyclic ketone 215 2  alkyl substitute 24 Calculated value 239nm Parent acyclic conjugated diene 215 2 alkyl subst. 10 2 ring residue 10 Exocyclic double bond 5 Calculated value 240

REFERENCE : 

REFERENCE INSTRUMENTAL METHOD OF CHEMICAL ANALYSIS by GURUDEEP R. CHATWAL, SHAM K ANAND 5th edition Page 2.162-2.167

THANK YOU : 

THANK YOU