How can we determine which of the above conpounds are aromatic . My teacher taught me to remove a hydrogen and shift the electrons but I did not understand it . Could someone help me so that i can learn and understand this subject better.
How many of the following are aromatic?
Among these compounds first four are aromatic where fifth compound is not aromatic.
- Coming to the first compound we have three π-bonds and a vacant orbital on B. So there are 6 electrons in conjugation and it obeys Hückel's rule. Hence, it is aromatic.
- Here we have two π-bonds and a lone pair on N. So there are six electrons in conjugation and hence, it is aromatic.
Note: Lone pair on right nitrogen is not involved in conjugation.
- Similar to 1 and 2, we have a vacant orbital on B, a lone pair on N and two π-bonds. So totally there are six electrons in conjugation and hence, it is aromatic.
- Form the following image you can understand why 4th compound is aromatic. Since there are six electrons in delocalisation where four electrons are from two π-bonds and two electrons from oxygen's lone pair.
I hope you can understand why 5th compound is not aromatic as it does not obey Hückel's rule.