Question

Write the structure and give the IUPAC systematic name of an alkane or cycloalkane with the formulas (a) C8H18 that has only primary hydrogen atoms, (b) C6H12 that has only secondary hydrogen atoms, (c) C6H12 that has only primary and secondary hydrogen atoms, and (d) C8H14 that has 12 secondary and 2 tertiary hydrogen atoms.

Answer 1

Primary hydrogens are those attached to a carbon which is attached to one other carbon atom Secondary hydrogens are those attached to carbon which are further attached to two other carbons. Tertiary hydrogens are those attached to carbon which are further attached to three other carbons. Examples of each is shown below: Secondary hydrogens H30—62-HC Primary hydrogens CH3 Primary hydrogens Tertiary hydrogen

(a) Structure of a compound having molecular formula C H, with only primary hydrogen atoms is shown below: . CH₃ CH3 H3C—¢- ¢-CH3 CH3 CH3 To write the IUPAC name, choose the longest carbon chain and number in such a manner that each substituent gets the lowest possible number position. CH3 CH3 _ 13 _ 4 H2C- -C- CH3 H3 CH3 CH₃

The longest chain has four carbo atoms called butane and four methyl substituents are present; two methyl at second position and two methyl at third position. The IUPAC name of the compound is, 2,2,3,3-Tetramethylbutane. (b) Structure of a compound having molecular formula C H, with only primary and secondary hydrogen atoms is shown below: ------------ The given molecule has a cyclobutane ring with two methyl substituents at first position. The IUPAC name of the compound is 1,1-Dimethylcyclobutane.

(c) that has 12 secondary and 2 tertiary Structure of a compound having molecular formula C H hydrogen atoms. This compound is a bicyclic compound with the bridged carbon atoms. It contains eight carbon atoms that is octane which is the root name and bicyclo' is used as prefix which is followed by three numbers separated by a dot and enclosed in squared brackets. Numbering of the cyclohexane ring would start from one of the bridged carbons.

The encircled carbon atoms are the bridge carbons. Count the number of atoms attached to the bridged carbons each time forming a ring. Since, three rings are formed the number assigned is [2.2.2] Therefore, the IUPAC name of the compound is Bicyclo [2.2.2]octane.