Question

6. Examine the following hydrocarbons and circle any that are aromatic. If a compound is not aromatic, briefly explain why. You may assume that each compound can adopt a planar conformation. coas as

Answer 1

To be aromatic, a molecule must meet the following four conditions:

• It must be a ring.

• It must be flat (planar).

• It must have in each atom of the ring a p orbital that’s orthogonal to the plane of the ring. In other words, no atom in the ring can be sp3 hybridized.

• It must have a Hückel number of pi electrons, following the 4n + 2 rule.

If the molecule meets the first three conditions, but only has 4n pi electrons, the molecule is anti-aromatic. If the molecule fails any or all of the first three conditions, then the molecule is non-aromatic

Pi Electron Counts

Integer (n)	Aromatic Numbers (4n + 2)	Anti-aromatic Numbers (4n)

0

2

—

1

6

4

2

10

8

3

14

12

4

18

16

5

22

20

WAV quesi's → non- aromatic S Page No. DateT Because ita compound does not have a continuous Using of conjugated p-orbitals in la planar confonation, then it is ze none romatic * 513 t i non aromatic Because hybridized. the marked carbon atom is op3 it is non-aromatic do aromatic 40+2 Here foun= 2 = 10. la Hence 10 electrons at which are having pi bond- 21 & The pi-elections here are - 9X2=8 So, as per the given table, this is anti- cromatic I . .111 TL Picetectromos 6X2 = 12 Anti-am Anti-aromatic pi-electionis . q 2 = 18 I. It follows unt2 unte. Aromatic Scann Cams

Page No. Date pi-electrons in a triple bond sare also 2. ... Total num ctrons = 6x2 = 12 .. According to the table for the table for the si electron my own the This compound is anti-aromatic. Scanned with CamScanner

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