Write structures for the following compounds.(a) 3-ethyl-4-methylhexane (b) 3-ethyl-5-isobutyl-3-methylnonane(c ) 4-tert-butyl-2-methylheptane (d) 5-isopropyl-3,3,4-trimethyloctane

Here's what I get  

Explanation:

(a) 3-Ethyl-4-methylhexane

The main chain is eight carbons long, with an ethyl group at C-3 and a methyl group at C-4

(b) 3-Ethyl-5-isobutyl-3-methylnonane

The main chain is nine carbons long, with an ethyl group and a methyl group on C-3 and an isobutyl group on C-5.

Note that the name isobutyl is acceptable in general use, but the preferred IUPAC name (PIN) for the group is now (since 2013) "2-methylpropan-2-yl".

The PIN for your compound is 3-ethyl-3-methyl-5-(2-methyl propan-2-yl)nonane.

(c) 4-tert-butyl-2-methylheptane

The main chain is seven carbons long, with a tert-butyl group at C-4 and a methyl group at C-2.

For some reason, the IUPAC has retained the name tert-butyl for the group, so the name you give is the PIN.

The prefix "tert" is written in italics.

(d) 5-isopropyl-3,3,4-trimethyloctane

The main chain is eight carbon atoms long, with two methyl groups on C-3 and one on C-4, and an isopropyl group on C-5.

The PIN for an isopropyl group is now "propan-2-yl", so the IUPAC name for your compound is 3,3,4-trimethyl-5-(propan-2-yl)octane.

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