Nomenclature and Isomerism

 

 

 

 

ROOTS

Longest unbranched carbon chain or ring

1C = METH

2C = ETH

3C = PROP

4C = BUT

5C = PENT

6C = HEX

 

 

 

 

-ANE

E.g alkanes – no double bonds

 

 

 

 

-ENE

E.g alkenes – one or double bond

 

 

 

 

-YNE

Triple bond – e.g alkynes

 

 

 

 

ALKYL GROUPS

Often called R or R’ if there is more than one

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FUNCTIONAL GROUPS

The reactive group

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ALKENES*

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ALKYNES*

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HALOALKANES*

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CARBOXYLIC ACIDS*;

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ACID ANHYDRIDES*

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ESTERS*

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ACYL CHLORIDES*

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AMIDES*

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NITRILES*

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ALDEHYDES*

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KETONES*

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ALCOHOLS*

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AMINES*

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ARENES*

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NUMBERS AND WORDS

Commas between numbers and hyphen between words and numbers

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ISOMERS

Compounds with the same molecular formular but different structural formular

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STRUCTURAL ISOMERS

Different functional groups;

Funtional groups attatched to the main chain at different points

OR they have a different arrangement of carbon atomes in the molecule

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STEREOISOMERISM

Two or more compounds have the same structural formula but they differ in the arrangement of the bonds

There are two tyeps; E-Z isomerism and optical isomerism

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E-Z ISOMERISM

Position of substituents at either side of a carbon molecule. If they are on the same side then Z (cis) if on opposite side then E (trans);

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only in double bonds, because substitutes joined by a single bond can rotate but there is no rotation around a double bond -so E/Z are seperate compounds

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OPTICAL ISOMERISM

Four different substituients attastched to one carbon atom; the tow isomers are mirror images of one another but not identical becasue they can’t be superimposed on one another

 

 

 

 

WHAT DO OPTICAL ISOMERS DO? 

They differ in the way they rotate the plane of polarisation of polarised light. Either clockwise or anticlockwise

 

 

 

 

CHIRALITY

Optical isomers are said to be chiral. The carbon that is bonded to 4 different groups is called the chiral carbon

 

 

 

ENANTIOMERS

The two optical isomers

 

 

 

 

ASYMMETRIC CARBON ATOM

The chiral carbon

 

 

 

 

OPTICAL ISOMERS STRUCTURES

3 dimensional structures 

 

 

 

 

OPTICAL ACTIVITY

Light passed through a polaroid, all vibrations are cut out except theose in one plane so it’s vertically polarised. effected differently by different optical isomers

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+ ISOMER

Rotates the plane of polarised light clockwise

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– ISOMER;

ROTATES THE PLANE OF POLARISED LIGHT ANTICLOCKWISE

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RACEMATE MIXTURES

50:50 Mixture of two optical isomers. Therefore the mixture is not optically active becasuet the effects cancel each other out

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WHEN A CARBON CHAIN NEEDS TO BE LENGTHENED

A nitrile group is added. This nitrile group will then be coverted into a carboxylic acid group by hydrolysis

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IN LIVING THINGS

Only one optical isomer is made. Because most naturally occuring molecules are formed by enzyme catalysts. The can only produce one of the possible optical isomer

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OPTICAL ISOMERS AND DRUGS

Some drugs require only one optical isomer

Others can deal with racemic mixtures

Drugs work by the active ingredient fitting the cell receptor. Receptors are 3D so only one pair of optical isomers will fit. Some cases one is active and the other is inactive, other times one is dangerous e.g. thalidomide

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THREE OPTIONS WITH DRUGS

Seperate the two isomers;

Sell the mixture as a drug (only if one is inactive, it’s wasteful though as half won’t work);

Design alternative synthesis of the drug that makes only the isomer that works

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