It is urgent please. How many stereogenic centres are there in these compounds , respectively?And i thought that for a stereogenic centre it must have 4 groups attached to it.But here they do not have 4 groups.

CH3-C(CH3)=N-OH and CH3-CH=N-OH

'x' gm of a compound A3B2C5 contains 'y' gm of A atoms

 

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how to represent the possible fischer projections for 2-bromohexane