3 Alkane(organic Chem) NJC

National Junior College SH1 H2 Chemistry 1 3 HYDROCARBONS - ALKANES AND CYCLOALKANES 3.1 INTRODUCTION Alkanes are the simplest of the homologous series of organic compounds and are also the least reactive hydrocarbons. Alkanes are saturated hydrocarbons as they contain only C −H and C −C single () bonds with a maximum of 4  bonds per carbon. All C atoms in alkanes are sp3 hybridised with each C atom in a tetrahedral geometry. Alkanes can be classified as acyclic (aliphatic, straight and branched chains) or cyclic closed rings. 3.1.1 Acyclic (non-cyclic) Alkanes Acyclic alkanes have the general formula CnH2n+2 and contain zig-zag chains of C atoms. Acyclic alkanes can be classified as straight and/or branched chains. methane butane 3-methylpentane CH4 Straight chain Straight chain Branched chain 3.1.2 Cyclic Alkanes (closed rings alkanes) Cyclic alkanes (cycloalkanes) have the general formula CnH2n (same as alkenes). Molecular formula Name Skeletal formula C3H6 cyclopropane C4H8 cyclobutane C5H10 cyclopentane C6H12 cyclohexane .

National Junior College SH1 H2 Chemistry 2 3.2 NOMENCLATURE OF BRANCHED CHAIN ISOMERS (IUPAC SYSTEM) Success criteria: • I can deduce the structure of an alkane from its given IUPAC name (and vice versa) The names of alkanes end with the letters ‘-ane’. The following are the names for the first 6 straight-chain alkanes. n Molecular formula Name Condensed Structural formula Skeletal formula 1 CH4 methane CH4 2 C2H6 ethane CH3CH3 3 C3H8 propane CH3CH2CH3 4 C4H10 butane CH3(CH2)2CH3 5 C5H12 pentane CH3(CH2)3CH3 6 C6H14 hexane CH3(CH2)4CH3 With branching, atoms or groups of atoms that make up the side chains have to be considered a substituent. The IUPAC name of an organic compound consists of a parent (or stem), a suffix and as many prefixes as necessary. Prefix(es) Parent Suffix How to name an organic compound 1 Identify the longest continuous carbon chain for the parent name. 2 Numbers carbon atoms in the longest chain nearer to the first branch point 3 Identify and label numbers on the substituents. If two or more substituents are present, cite them in alphabetical order. The number prefixes di-, tri-, tetra-, etc. are ignored in alphabetising. Substituents Longest continuous carbon chain bearing the principal (most important) functional group Principal functional group

National Junior College SH1 H2 Chemistry 3 Checkpoint 1 1 Determine if each alkane is named correctly using IUPAC nomenclature. If the naming is incorrect, give the correct IUPAC name. Organic compound Is naming correct? (Y / N) Correct IUPAC name (if relevant) 2-methyl-4-ethylpentane 2,2-methylpropane 4,4-dimethyl-3-ethylpentane 2,2,4-trimethylpentane 2 Draw the skeletal formula of 2-ethyl-1,1-dimethylcyclohexane.

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