chains,rings,branches

Asked by  | 7th Apr, 2008, 10:44: PM

Expert Answer:

 Alkanes are types of organic hydrocarbon compounds which have only single chemical bonds in their chemical structure. Cycloalkanes consist of only carbon (C) and hydrogen (H) atoms and are saturated because there are no multiple C-C bonds to hydrogenate (add more hydrogen to). A general chemical formula for cycloalkanes would be CnH2(n+1-g) where n = number of C atoms and g = number of rings in the molecule. Cycloalkanes with a single ring are named analogously to their normal alkane counterpart of the same carbon count: cyclopropane, cyclobutane, cyclopentane, cyclohexane, etc. The larger cycloalkanes, with greater than 20 carbon atoms are typically called cycloparaffins.

The classifications for hydrocarbons defined by IUPAC nomenclature of organic chemistry are as follows:

  1. Saturated hydrocarbons (alkanes) are the most simple of the hydrocarbon species and are composed entirely of single bonds and are saturated with hydrogen; they are the basis of petroleum fuels and are either found as linear or branched species of unlimited number. The general formula for saturated hydrocarbons is CnH2n+2 (assuming non-cyclic structures).
  2. Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Those with one double bond are called alkenes, with the formula CnH2n (assuming non-cyclic structures). Those containing triple bonds are called alkynes, with general formula CnH2n-2.
  3. Cycloalkanes are hydrocarbons containing one or more carbon rings to which hydrogen atoms are attached. The general formula for a saturated hydrocarbon containing one ring is CnH2n
  4. Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring.

Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene).

Simple branched alkanes are really alkanes with alkyl substituents.  The principles covered here will apply to other substituted systems in general.

The substituent is named in a similar way to the parent alkane. It is named based on the number of carbon atoms in the branch plus the suffix -yl.  

CH3- methyl
CH3CH2- ethyl
CH3CH2CH2- propyl

In general an alkane type substituent becomes an alkyl group (often represented as "R-")

The name is then constructed in the standard way with locant + substituent prefix + root name  based on the basic rules.
CH3CH2CH2CH(CH3)2 

  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C5 therefore root = pent
  • The branch is a C1 alkyl group i.e. a methyl group
  • The first point of difference rule requires numbering from the right as drawn, the substituent locant is 2-
2-methylpentane

Answered by  | 11th Jun, 2008, 06:57: PM

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