Question #16b44

1 Answer
Dec 9, 2016

Answer:

The order is #("CH"_3)_3"C-" > "CH"_2"=CH-" > ("CH"_3)_2"CH-" > "CH"_3"CH"_2"-"#

Explanation:

The Cahn-Ingold-Prelog order is based on the atomic numbers of the atoms attached to the chiral centre.

If there is a tie, we go one atom further out and keep going until the tie is broken.

In this problem, the atoms attached to the chiral centre are all carbon atoms, for
a 4-way tie.

To break the tie, we look at the atoms that are directly attached to these carbons.

First trial

#"C1"# of the vinyl group is attached to another carbon by a #"C=C"# double bond.

Each carbon in the double bond counts as two carbons.

So, #"C1"# is attached to #"C, C"#, and #"H"#, written as (#"C,C,H"#) with the atoms listed in order of decreasing atomic number.

#"C1"# of the isopropyl group is attached to #"C, C"#, and #"H"# (#"C,C,H"#).

#"C1"# of the tert-butyl group is attached to (#"C,C,C"#).

#"C1"# of the ethyl group is attached to (#"C,H,H"#).

We now compare the atoms in parentheses and look at the first point of difference.

We find tert-butyl (#"C,C,C"#) > vinyl (#"C,C,H"#) = isopropyl (#"C,C,H"#) > ethyl (#"C,H,H"#).

So, tert-butyl is Priority 1 and ethyl is Priority 4, but vinyl and isopropyl are tied in the middle.

Second trial

To break the tie, we look at the atoms directly attached to #"C2"#.

#"C2"# in the vinyl group is attached to (#"C,H,H"#).

#"C2"# in the isopropyl group is attached to (#"H,H,H"#).

So the vinyl group wins and gets Priority 2, and the isopropyl group is Priority 3.

The order is #("CH"_3)_3"C-" > "CH"_2"=CH-" > ("CH"_3)_2"CH-" > "CH"_3"CH"_2"-"#