Nomenclature and Isomerism

HideShow resource information

Naming Organic Compounds

1 = Meth-            2 = Eth-             3 = Prop-             4 = But-             5 = Pent-             6 = Hex-

If they are branched alkanes they are.. EthYL....  

HALOALKANES:    Flurine = Fluoro-     Chlorine = Chloro-    Bromine = -Bromo     Iodine = Iodo-

ALKENES: At least one double bond between their carbon atoms. Named the same way but end in -ene  e.g Pent-1-ene (Double bond is on the first carbon)

ALCOHOLS: They are named as above but end in -ol . If there are 2 -OH groups it is -diol and 3 then it is -triol

PRIMARY, SECONDARY AND TERTIARY ALCOHOLS: Depends on which carbon the -OH is on. Primary; notion 1   and the -OH group is attached to a carbon with 1 alkyl group attached.         Secondary; Notation 2   and the -OH is attached to a carbon with 2 alkyl groups attached.           Tertiatry; Notation 3   and the -OH group is attached to a carbon with 3 alkyl groups attached.

1 of 6


MOLECULAR : e.g. C6H12   (Hexene)

STRUCTURAL : e.g.  CH3CH2CCH2CH2CHCH2   (Hex-1-ene)

DISPLAYED :  How the atoms are arranged and all the bonds between.   (draw this one)




SKELETAL : Shows bonds of carbon skeleton only, with any dunctional groups.




EMPIRICAL : Simplest ratio of whole number atoms. e.e. Hex-1-ene --> C6H12 --> CH2

2 of 6

Isomerism - Structural

Structural Isomers are connected in different ways, but they have the same molecular formula.

CHAIN: Have different arrangments of the carbon skeleton :



POSITIONAL: Have the same skeleton and the same atoms or groups of atoms attached. Difference is the atom or group of atoms are attached to a different carbon atom:



FUNCTIONAL: Same atoms arranged in different functional groups:



3 of 6

Isomerism - Stereoisomers

Stereoisomers have the same structural formula but different arrangement of atoms in space.

A double bond has a fixed position- Cant rotate the rest of the molecule around it. Because of the lack of rotation, some alkenes have E/Z-Isomers. These occur when a double bond has 2 different atoms or groups attached to it.







Optical Isomerism is another form of stereoisomerism.....

4 of 6

Optical Isomerism

Optical Isomers have a chiral carbon atom. --> A chrial carbon atom is one that has 4 different groups attached to it.

ENANTIOMERS: Possible to arrange the groups in 2 different ways around chiral carbon so 2 different molecules are made (they are enatiomers or optical isomers). Enantiomers are mirror images that cannot be superimposed!




OPTICAL ACTIVITY: Optical Isomers are optically active --> they rotate plane-polarised light.    Plane-Polarised Light; when light vibrates in the same plane ( only up or down or side to side)  Rotation of Plane-Polarised Light; Optically active isomers rotate the light in different directions . One in a clockwise-direction the other in an anti-clockwise direction

5 of 6

Optical Isomerism Continued

Racemates                                                                                                                                           A racemate (or racemic mixture) contains equal quantities of each enantiomer of an optically active compound. ---> they dont show optical activity as the 2 enantiomers cancel each others light-rotating effect

Chemist often react 2 chiral things togetherand get a racemic mixtureof a chiral product.  Because when you react 2 molecules there is and equal chance of formin each of the enantiomers.

Pharmaceutical Drugs

Drugs work by changing chemical reactions that happen in the body. Enantiomer has a specific shape to fit to the active site, only one enantiomer with do a certain job.

Possible to use a racemate mixture of the drug to treat a patient. May need to take double the dose to acheive the same effect as the 'pure' enantiomer version.

using a racemic mixture as a drug has benefits : no need to seperate out enantiomers, reducing the difficulty and the cost of producing the drug.

6 of 6


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Nomenclature and Isomerism resources »