Question

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5. Draw and name an example of any ether that contains at least one stereogenic center. 6. Using a substitution reaction, synthesize hexyl isobutyl ether.

Answer 1

5) Ether is an organic compound in which one oxygen connected to the alkyl or aryl groups (R-O-R'). Here we need to write and name the ether compound which contains minimum one stereogenic center in it.

Stereogenic center means, at any point of molecule which is sp3 hybridised and has different groups in which if we interchange any of two groups, it gives a stereoisomer.

  

Cн 3 -CHз 5 (1S,2R)-1-ethoxy-2-methoxycyclopentane

In the above example, the compound has two ether groups and two stereogenic center at 1st and 2nd position of cyclopentane ring. At 1st position it has 'S' configuration (anti-clockwise direction of groups according to its weight priority) and 2nd position it has 'R' configuration (clockwise direction of groups according to its weight priority.

Therefore, the name of the compound is (1S,2R)-1-ethoxy-2-methoxycyclopentane and its structure is written above.

6) Before writing the synthesis, first we need to draw the structure of the ether compound using given name. Name of the ether molecule is hexyl isobutyl ether. Here, oxygen is connected to a hexyl group (6 membered alkane group) and a isobutyl group (2-methylpropyl group).

Hexyl isobutyl ether

Now we have to outline the synthesis of the above ether using substitution reaction. In the substitution reaction one functional group in a molecule replaced with another functional group.

In this synthesis of ether, the substitution reaction (S_N2) will takes place in between a deprotonated alcohol (alkoxide) and an alkyl halide in the presence of a solvent. Usually solvent is taken here is the conjugate acid of the alkoxide (alcohol). This reaction is also called as Williamson ether synthesis.

Note : Here the alkoxide can be a primary, secondary or tertiary or aryl alcohol. But alkyl halide must be a primary alkyl halide.

So, in this synthesis, the long 6 member chain hexyl group is taken as alkyl halide (hexyl bromide). Because it is a primary akyl halide. And another fragment isobutyl group taken as an alkoxide (isobutyl alkoxide). Here the solvent is the conjugate acid of isobutyl alkoxide that is isobutyl alcohol. So, these two reactants will reacts together by the elimination of bromide ion and formation of ether molecule takes place as shown below.

Н.С Na O Br + 1-bromohexane Isobutyl alkoxide (primary alkyl halide) но Isobutyl alcohol (solvent) NaBr Hexyl isobutyl ether