Chemistry [[Module Three]] Nomenclature and Isomerism

[[Isomerism]]

Occurs when molecules with the same molecular formula have their atoms aranged in different ways. It is sub divided.

[[Structural Isomerism]]


COMPOUNDS WITH THE SAME MOLECULAR FORMULAE BUT WITH DIFFERENT STRUCTURES


[Chain Isomerism]

occurs when there are two or more ways of arranging the carbon skeleton of a compound. The isomers have similar chemical properties byr slightly different physical properties. Branched isomers have smaller volumes, weaker van der waals and threrefore lower boiling points.


Isomers of C5H12:










[Position Isomerism]



Isomers have the same carbon skeleton and the same functional group but the functional group is joined at different places on the carbon skeleton.



CH3CH2CH2BR = 1-bromopropane
CH3CHBrCH3 = 2-bromopropane



CH2=CHCH2CH3 = but-1-ene
CH3CH=CH2 = but-2-ene



They have similar chemical properties but the different positions cause differences in physical properties.



[Functional Group]



Isomers have different functional groups
they have different physical and chemical properties.



C3H6O:



CH3CH3CHO or CH3COCH3
propanal propanone



C3H6O2



CH3CH2COOH or CH3COOCH3 or HCOOCH2CH3
propanoic acid methyl ethanoate ethyl methanoate



[[Stereoisomerism]]



MOLECULES WHICH HAVE THE SAME STRUCTURAL FORMULA BUT THEIR BONDS ARE ARRANGED DIFFERENTLY IN SPACE



[Geometrical (Cis-Trans0 Isomerism]



Carbon carbon double bonds cannot rotate died to electron clouds above and below plane of the bond.
If there are two different groups at each end of the double bond then cis-trans isomerism results.


Cis: Two identical groups on the same side of the double bond
Trans: Two identical groups on oppersite sides of the double bond



Geometrical Isomerism is not possible when there are two identical groups on the same carbon.