The Octant Rule

Presented ByPresented By:-

Rahul SharmaRahul Sharma

M. Pharm – I (Pharmaceutics)

Submitted ToSubmitted To:-

Dr. G. S. GadaginmathDr. G. S. Gadaginmath

Department Of Pharmaceutical Chemistry

Set’s College Of Pharmacy (Dharwad)

2/9/2010 1

Contents Contents :-:-

• IntroductionIntroduction

• Facts Facts

• Statement of octant ruleStatement of octant rule

• Applications with examplesApplications with examples

• Summary Summary

• QuestionsQuestions

• References References

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Introduction Introduction • It is an empirical rule that establishes an

absolute configuration or stereochemistry from the sign and intensity of cotton effect

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Facts Facts :-:-• Octant rule was developed by Djerrasi and Octant rule was developed by Djerrasi and

coworkerscoworkers• It relates the sign and amplitude of cotton It relates the sign and amplitude of cotton

effect exhibited by an optically active effect exhibited by an optically active saturated ketone to the spatial orientation of saturated ketone to the spatial orientation of atoms about the carbonyl functionatoms about the carbonyl function

+ -

- +

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Octant rule states that Octant rule states that :-:-• Substituents lying in the co-ordinate planes Substituents lying in the co-ordinate planes

make up no contribution to the rotatory make up no contribution to the rotatory dispersiondispersion

• Substituents lying the back upper left and back Substituents lying the back upper left and back lower right make positive contributionlower right make positive contribution

• Substituents in the upper right and back lower Substituents in the upper right and back lower left make negative contributionleft make negative contribution

(+) (-)

(-) (+)

Back OctantsBack Octants

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For a cyclohexane ring:-For a cyclohexane ring:-

Carbon atom number Total cotton effect

C1 0+0=0

C2 0+(-)= -

C3 (+)+(+) = +

C4 0+0=0

C5 (-)+(-)= -

C6 (+)+0= +

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InformationInformation:• Substituents in nodal planes contribute nothing• Substituents within octant contribute sign of that

octant• At a time 4 octants are considered and rest 4

are empty

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ExampleExample• 3-methyl hexanone• Equatorial confirmation more stable• Atoms 2, 4, 6 – in nodal planes so no

contribution

• Atoms 3 and 5 cancel each other but the methyl substitution, if axial leads to negative effect and if it is equatorial then the net effect is positive contribution 8

APPLICATIONSAPPLICATIONS1.1. Prediction of cotton effectPrediction of cotton effect

Example : 5Example : 5αα – cholestan – 6 – one – cholestan – 6 – one

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2. 2. Determination of configurationDetermination of configuration:-:-

Example: Example: trans - 10 – methyl – 2 – decalone trans - 10 – methyl – 2 – decalone

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3. 3. Study of conformational mobilityStudy of conformational mobility:-:-

Example: Example: 2- chloro – 5 – methylcyclohexanone 2- chloro – 5 – methylcyclohexanone

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Few back octant projections of some cholestanonesFew back octant projections of some cholestanones

Ketone α Octant Diagram Prediction

2 – cholestanone +121 7, 19, ring C, D

(+)ve

3 – cholestanone +65 6, 7, 15, 16 (+)ve

4 - cholestanone -94 19, ring C, D (-)ve

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SummarySummary:-:-

• It is an empirical rule that establishes an absolute configuration or stereochemistry from the sign and intensity of cotton effect

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References :-References :-• Kemp WilliamKemp William; “ Organic Spectroscopy “;3; “ Organic Spectroscopy “;3rdrd

edition – 1991; Palgrave, New York; Page No. edition – 1991; Palgrave, New York; Page No. - 279-280- 279-280

• Kalsi P.S.Kalsi P.S.; “ Spectroscopy of Organic ; “ Spectroscopy of Organic Compounds”; 6Compounds”; 6thth edition – 2004; New Age edition – 2004; New Age International (p) Ltd, New Delhi; Page No. – International (p) Ltd, New Delhi; Page No. – 616-623616-623

• Internet Internet (google.co.in)(google.co.in)

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Important QuestionsImportant Questions• Predict the sign of cotton effect for following Predict the sign of cotton effect for following

compounds using octant rule.compounds using octant rule.• Explain octant rule and its applications with Explain octant rule and its applications with

suitable examples . suitable examples .

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