Question

Question #16b44

Answer 1

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"-"`