INTRODUCTION TO ORGANIC CHEMISTRY organic chemistry is the most important branch of chemistry - but of course it would be nothing without the many other areas of chemistry -in fact all branches of chemistry should not be viewed in isolation, even though they may often be taught in isolation
organic chemistry is all around us, life is based on organic chemistry, the clothes we wear, the drugs we take, the cars we drive and the fuel that propels them, wood, paper, plastics and paints
organic chemistry is the study of compounds containing carbon
the ability of carbon to form as many as 4 strong bonds to many other atoms, e.g., carbon, hydrogen, oxygen, nitrogen, halogens, sulphur, phosphorus ensures a virtual infinite number of possible compounds the constituent atoms and their exact combination determines the chemical and physical properties of compounds and hence their suitability for applications
the organic chemistry for this first semester will consist of the following topics
general introduction - structure and bonding, examples of
organic compounds, nomenclature, examples of organic reactions, an introduction to reaction mechanis
ms
Alkanes - physical properties, synthesis, chemical properties Alkenes - physical properties, synthesis, chemical properties Alkynes - physical properties, synthesis, chemical properties
all examined as part of module 06510
recommended texts
Organic Chemistry by Solomons and Fryhle (8th edition) 2004
Organic Chemistry by Maitland Jones (3rd edition) 2004
Organic Chemistry by Clayden, Greeves, Warren, Wothers 2001
H C
H H H C
H C
H
H
hydrocarbons - contain carbon and hydrogen only TYPICAL ORGANIC COMPOUNDS STRUCTURES AND NOMENCLATURE
H C H H
C
H H
C H H
butane
CH 3CH 2CH 2CH 2CH 3
pentane CH 3(CH 2)4CH 3
hexane
hept, oct, non, dec, undec, dodec,
what about branched chain systems?
take the longest chain - C 5 - hence pentane,number the chain so that the substituents have the lowest possible numbers - hence
there are many different ways to draw chemical structures, often it does not matter which is used, but sometimes a full structure will be required if reaction mechanisms are being considered, for example
reactive carbonyl speciesthe nomenclature of organic compounds follows the IUPAC system -International Union of Pure and Applied Chemistry
first important IUPAC rule - names are based on the number of carbon atoms present in the longest possible chain
propane
methane ethane 2,3-dimethylpentane note the commas and hyphens - very important not 3,4-look carefully, you might think a pentane? but no the longest chain is six - hence hexane - what is the substituent? ethyl, at the 3- position - hence
3-ethylhexane 2H 5
not 3-propylpentane!!!same rules as above, then list substituents alphabetically (ignore prefixes such as di and tri; i.e., dimethyl comes after ethyl) - hence
4-ethyl-2-methylhexane
4-chloro-2-ethyl-1-methylcyclohexane
same rules for cyclics
1-ethyl-3-methylcyclohexane
alkanes - fully saturated, all single bonds, chain and cyclic
H 3C
CH CH 3
CH
CH 3
H 3H 3C
CH CH 3
H 3C CH 3
CH 3
H 3C
C CH 3
CH 3
21-methylethyl  or isopropyl
1-methylpropyl  or sec -butyl
1,1-dimethylethyl  or tert -butyl
2-methylpropyl  or isobutyl
hydrocarbon sub-units with trivial names retained by IUPAC
2,2-dimethylpropyl  or neopentyl
this is the only five-carbon unit with a trivial name allowed by IUPAC
the hydrogen atoms of an alkane are classified according to their position - primary (1°), secondary (2°), tertiary (3°)
1° hydrogen atoms
X
2
X
3° hydrogen atom
2° hydrogen atoms
as we shall see later, the 'removal'of a hydrogen atom leaves a
sub-unit that is classified 1°, 2° or 3°as appropriate - of great significance in organic reactions
X
trivial names persist in many cases beacuse they are convenient, but often difficult to deal with - in some cases the trivial names are common and have been retained under the IUPAC system
other common sub-units
vinyl allyl propargyl
benzyl the above sub-units are also of significance in organic reactions
but-1-ene
CH3CH=CHCH2CH2CH3
trans-but-2-ene cis-but-2-ene
note from butene we get
possible isomers, but-1-ene
and but-2-ene, and because
the π-bond restricts rotation
there are two isomers of
but-2-ene (cis and trans)
general formula,
cis or trans not defined
definitely trans
obvious why
3
not trans-hex-4-ene
trans-hex-2-ene
4-methylpent-3-en-2-ol
note the same
prefix as for
alkanes not 2-methylpent-2-en-4-ol
2
CH3
speaking of cyclics!
propene
very similar to acyclic alkenes,
but where the numbering is set
by the double bond at position 1
there is no need to include it
3-methylcyclohexene
but-1-ene
1-butene (USA)
H3
C C
CH3
CH3
3
H
H
note that the numbering is usually based on the position of the
double bond - not substituents, hence
not trans-2,2-dimethylhex-4-ene
lowest possible number for double bond is chosen
trans-5,5-dimethylhex-2-ene
but not for alcohols!!!, which we have not even mentioned yet,
perhaps you know what they are!!!
the nomenclature of alkenes follows the IUPAC system and is very
similar to that of alkanes - really very easy with experience
alkenes - unsaturated, C=C double bond, chain and cyclic
ethene
cyclohexene
2-methylcyclohex-2-en-1-ol
not 2-methylcyclohex-1-en-3-ol
C C H
H C C H
CH3C C CH2CH2CH3
CH3
C C CH2CH2OH
H
ethyne hex-2-yne
as for alkenes, with alcohols the OH takes
preference for the numbering
rules on branching just the same as for alkenes
propyne
not hex-4-yne
but-3-yn-1-ol
aromatic systems - benzene rings
the nomenclature of alkynes follows the IUPAC system and is very
similar to that of alkanes and alkenes - really very easy with experience alkynes - unsaturated, C≡C triple bond, chain and cyclic (rare)
benzene is a simple aromatic system and extremely common, naming is very easy!
bromobenzene
not methylbenzene
some suffixes have higher priorities than others
which forces the lower one to become a prefix
benzonitrile
not cyanobenzene
ethylbenzene
most substituted benzenes are named easily as
a benzene derivative - but some are not!!
nitrobenzene
a double bond takes preference
over a triple bond for numbering
pent-1-en-4-yne
not pent-4-en-1-yne
1-bromo-3-nitrobenzene
substituents are listed alphabetically -
as seen for other systems
2-hydroxybenzonitrile
not 2-cyanophenol
phenol
not hydroxybenzene

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