Question

22. Which of the following compounds is(are) conjugated diene(s)? II III IV a. ll only b. I and III c. I and IV d. II, Ill, and IV 23. Vitamin D, has the following structure. Classify the circled pi-bond in vitamin D, as conjugated, cumulated or isolated a. Conjugated b. Cumulated c. Isolate 24. What is the IUPAC name for the following compound? a. (22,42,6E)-3,4,7-trimethylocta-2,4,6-triene b. (2,4,6E)-2,5,6-trimethylocta-2,4,6-triene c. (25,4Z)-3,4,7-trimethylocta-2,4,6-triene d. (48,6E)-2,5,6-trimethylocta-2,4,6-triene

Answer 1

First let us understand what are different types of dienes

A diene is a molecule that has 2 double bonds.

A conjugated diene is a molecule where 2 double bonds are separated by a single bond.

Non conjugated or isolated diene is a molecule where two double bonds are separated by more than 1 single bond ( separated by at least 2 single bonds).

Cumulated diene is a molecule where the two double bonds are present on the same carbon.

Question 1

In case I and III, there are two single bonds in between the double bonds. So these are isolated dienes.

In case II and IV there is only one single bond between the two double bonds. So II and IV both are conjugated dienes.

Question 2

In case of vitamin D3 structure, the circled double bond is separated from another double bond by a single bond. So this is also a conjugated double bond

Dienes == 65 y 2 Conjugated Single bond between 28 3 separates two double bonds Isolated a single bonds - Cumulated between 2,384 a double separate two bonds on sam double bonds carbon. 1 single bond a single bonds between double bonds between double bonds Da W 1 single bond between afb 1 single bond between b&c These are conjugated dienes

Question 3

In this structure the numbering starts so that the functional groups should get the lowest possible numbers. (If you start from the opposite end, then the double bonds will have same numbers 2,4,6 but the methyl groups will have higher number 3,4,7). So this is how the numbering needs to be done.

Now for Giving E/Z notation, the 4 groups attached to thw double bond should be different. When we look at the double bond at 2 position, it has 2 identical methyl groups. So this will not display any E/Z isomers.

Double bonds at 4 and 6 position will display E/Z isomerism.

So the name of this structure is (4E,6E)-2,5,6-trimethylocta-2,4,6-triene

1 single oond between De These are conjugated dienes " a, bare identical. No Elz at 2 position Pl is the first priority P2 is lower priority Both Pl are on opposite side. so E isomer at 4 position I P. Here also P1 2 side. So. This is are on opposite also t somer