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1-Given that two π bonds conjugated together have a lower energy than two separate π bonds ( Fig . 1.32 ) and a C - H bond conjugated with π bond also lowers the energy ( Fig . 2.11 ) , explain why two C - H bonds conjugated to each other are not stabilised ?.

2- Explain why silylamines are weaker bases than ammonia and why

hexa-phenylsiloxane ( Ph3zSi )2O is linear .

3-Explain why , when the substituent Y in an allylic ether is an alkyl group the preferred conformation 2.106 , but when it is a carbonyl or nitrile group , the preferred conformation is 2.107