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Organic compounds: Compounds containing the element carbon.

Special characteristics of many organic compounds are chains or rings of carbon atoms bonded together.
These provide the basis for naming, and the presence of many carbon-hydrogen bonds.
The valency of carbon in organic compounds is 4.

Hydrocarbons: Compounds containing only the elements C and H.

Straight chain hydrocarbons are named according to the number of carbon atoms.

Saturated compound: One having only single bonds 
Example: ethane, C₂H₆
Saturated hydrocarbons are also known as alkanes.

Systematic nomenclature is largely based on the above series of saturated alkanes with the number of carbon atoms associated with the stems:

	meth-,	(1);
	eth-,	(2);
	prop-,	(3);
	but-,	(4);
	pent-,	(5);
	hex-,	(6);
	hept-,	(7);
	oct-,	(8);
	non-,	(9);
	dec-,	(10);
	alk-,	(general);

The ending -ane means no unsaturation (no double or triple bonds). Alkanes may be non-cyclic (acyclic) or cyclic (contain rings). 
The general formula for an acyclic alkane is C_nH_2n+2 and for one containing one ring C_nH_2n. 
In cyclic alkanes the stem gives the number of carbon atoms in the ring. 
Example: c-C₆H₁₂ is cyclohexane, where c- means cyclic

Unsaturated compound: A compound with one or more multiple (double or triple) bonds.
Example: ethene (ethylene), CH₂=CH₂ .

Alkene: A hydrocarbon containing a double bond
Example: C₃H₆, CH₃-CH=CH₂, propene.

Alkyne: A hydrocarbon containing a triple bond
Example: C₄H₆ or CH₃CH₂C≡CH, butyne.

The endings -ene and -yne are for the double or triple bond respectively.
The general formula C_nH_2n+2 loses two Hs for each ring or each double bond and four H's for each triple bond. 
The position of the multiple bond is shown by a number in the name, numbering from the end of the chain to give the smallest number. 

Alkyl group: In general, an alkane minus one hydrogen atom and represented by R.
Examples:

CH₃- is methyl (sometimes shown as Me);
CH₃CH₂- is ethyl (sometimes shown as Et);
CH₃CH₂CH₂- is propyl (sometimes shown as Pr); 
CH₃CH₂CH₂CH₂- is butyl (sometimes shown as Bu).

In straight chain alkanes the non-terminal carbon atoms are bonded to two other carbon atoms. In abranched alkane one or more carbons are bonded to three or four other carbon atoms.

Primary carbon atom: A carbon atom bonded to only one other C atom.
Secondary carbon atom: One bonded to two other C atoms.
Tertiary carbon atom: One bonded to three other C atoms.
Quaternary carbon atom: One bonded to four other C atoms.
looking at primary, secondary, tertiary, quaternary carbons

Branched hydrocarbons are named after the longest chain (saturated) or the longest chain containing the double or triple bond (unsaturated) with the branched group given by its alkyl name
Example: CH₃C(CH₃)₂CH₂CH₃ is 2,2-dimethylbutane; .

Isomers: Compounds with the same molecular formula but with their atoms arranged differently
Example: hexane and 2,2-dimethylbutane, both C₆H₁₄.

Constitutional (structural) isomers: Isomers having their atoms joined together in a different sequence. 
Some chemists restrict this term for isomers which have different functional groups
Example: hexene and cyclohexane. 
They would classify isomers containing the same functional groups as positional isomers 
Examples: 2-methylpentane, CH₃CH(CH₃)CH₂CH₂CH₃ and 
3-methylpentane, CH₃CH₂CH(CH₃)CH₂CH₃).

Organic compounds are classified by the functional groups they contain.

Functional group: An atom or group of atoms which give the compound distinctive chemical properties.
Example: -Cl, -OH, >C=C<, -CO₂H. Thus all organic compounds except saturated hydrocarbons have one or more functional groups. The functional group determines the class of compound. In nomenclature the functional group may be identified by a prefix, a suffix, or by the class of compound. (See below)

Common functional groups and classes of compounds are:

-F, fluoro-; -Cl, chloro-; -Br, bromo-; -I, iodo-; generally called haloalkanes (prefix) or alkyl halides(class of compound)
CH₃CH₂Cl is chloroethane or ethyl chloride.
CH₃CHFCH₂CH₃ is 2-fluorobutane or secondary butyl fluoride..

-OH, hydroxy-, giving rise to alcohols. The -OH group can be named as the prefix hydroxy-, as the suffix -ol replacing the -e of the alkane or as an alcohol. 
Examples: CH₃CH(OH)CH₂CH₃ is butan-2-ol or secondary butyl alcohol;
(CH₃)₃COH is 2-methylpropan-2-ol or tertiary butyl alcohol.

-NH₂, amino-, giving rise to amines. The -NH₂ group can be named as the prefix amino-, with the suffix -amine replacing the -e of the alkane or as an amine.
Example: CH₃CH₂NH₂ is aminoethane, ethanamine or ethylamine. 
Amines can be considered as ammonia with hydrogens replaced by alkyl groups. If just one H is replaced the amine is a primary amine, as above. If two hydrogens are replaced the amine is a secondary amine 
Example: CH₃CH₂NHCH₃, N-methylethanamine 
(the N shows the methyl substituent is bonded to nitrogen) or ethyl methyl amine. 
If all three hydrogens are replaced the amine is a tertiary amine 
Example: (CH₃)₃N is trimethylamine.

(Note that for alkyl halides and alcohols 1^o, 2^o or 3^o refers to the carbon atom to which the halo or hydroxy group is attached.
For amines it refers to the number of alkyl groups on the nitrogen.
Thus (CH₃)₃COH is a tertiary alcohol,
but (CH₃)₃CNH₂ is a primary amine.)
some primary, secondary, tertiary alcohols and amines

	>C=O, carbonyl. If this is at the end of a chain the compound is an aldehyde, and named with the suffix al  We are looking at the structural formula of propanal or  propyl aldehyde.
	If the CO group is not at the end of a chain the compound is aketone, and named with the suffix -one pentan-3-one, (or diethyl ketone) is shown.  Propanone (dimethyl ketone) is commonly called acetone.
	carboxyl, giving rise to carboxylic acids.  The suffix −oic and the word acid are used in naming. CH3CH2CH2CO2H is called butanoic acid. Methanoic acid, HCO2H, is commonly called formic acid,  Ethanoic acid, CH3CO2H, is commonly called acetic acid. The group is also often written as −COOH instead of −CO2H. The CH3CO− group is commonly called the acetyl group.  RCO− is an acyl group.

The product of the reaction of a carboxylic acid with a base is a carboxylic acid salt, an ionic compound. The name of the cation is given first followed by the acid with the suffix -oate replacing -oic. 
Examples: CH₃CH₂CH₂CO₂¯Na⁺ is sodium butanoate; 
CH₃CO₂¯NH₄⁺ is ammonium ethanoate or ammonium acetate. 
The general name for the anion is carboxylate.

When the OH of the carboxyl group is replaced by another group the compond is a carboxylic acid derivative. If the OH is replaced by OR of an alcohol the compound is called an ester. The R group is given first followed by the acid with the suffix -oate replacing -oic 
Example: CH₃CH₂CO₂CH₂CH₃ is ethyl propanoate.
When the OH group is replaced by NH₂ the compound is a primary amide. The suffix -amidereplaces -oic.
Example: CH₃CONH₂ is ethanamide, more commonly called acetamide. 
If the OH has been replaced by an RNH the compound is a secondary amide, or by an RR'N group a tertiary amide, and the alkyl group of the amine named as such with the prefix N to show it is bonded to the nitrogen atom 
Example: CH₃CH₂CONHCH₃ is N-methylpropanamide. 
If the OH has been replaced by a halo group the compound is an acyl halide, -oic becoming -oyl 
Example: CH₃CH₂COCl is propanoyl chloride. 
If the OH has been replaced by a carboxylate group, OCOR, the compound is an acid anhydride. 
Example CH₃COOCOCH₃ is ethanoyl anhydride or acetic anhydride. An anhydride in general is a substance formed by removing the elements of water from the compound. 
Example 2CH₃CO₂H  CH₃COOCOCH₃ + H₂O

Multifunctional compound: A compound with more than one functional group.

Nomenclature of multifunctional compounds: The longest chain containing the suffix is chosen, the priority for choosing the suffix being carboxylic acid, -CO₂H, > carboxylic acid derivative, -COX > aldehyde, -CHO > ketone, -CO-, > alcohol, -OH > amine, -NH₂. The second and other groups are labelled as substituents.
some examples of multifunctional compounds

For compounds with larger carbon skeletons a further condensation of structural may be used.

	represents propylcyclohexane. Each line represents two carbon atoms joined by a single bond, and hydrogens which are present are not shown. The number of Hs is such to satisfy the valency of carbon, 4.
	is butylbenzene.

Benzene is C₆H₆ and is the parent of aromatic compounds. Each carbon in the benzene ring has one hydrogen attached. As a second resonance structure with the double bonds in the other three positions can be drawn, the resonance hybrid of benzene is often represented as a hexagon with a circle inside:

i.e. 

Aromatic compound: An organic compound containing one or more benzene rings.

Phenyl group: Benzene minus one hydrogen, C₆H₅- (sometimes shown as Ph). 
Example: C₆H₅CH₂CH₂CO₂H is 3-phenylpropanoic acid.

Benzyl group: C₆H₅CH₂- 
Examples C₆H₅CH₂Cl is benzyl chloride; 
C₆H₅COOH is benzoic acid.

Many substituted benzenes have common names. PhOH is phenol, PhCH₃ is toluene; PhNH₂ is aniline; PhCH=CH₂ is styrene.

Vinyl Group: Ethene minus a hydrogen, CH₂=CH-. 
Examples: CH₂=CHCl is vinyl chloride, CH₃COOCH=CH₂ is vinyl acetate. 
Vinyl compounds are the monomers of vinyl polymers. 
Example: PVC, polyvinyl chloride; PVA, polyvinyl acetate.

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