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Write structures of various carbocations that can be obtained from 2-methylbutane . Arrange these carbocations in order of increasing stabililty. |
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Answer» Solution :`square ` 2-methyl butane has four different sets of EQUIVALENT H-atoms . `CH_(3) - underset (CH_(3))underset (|)(C)H- CH_(2) - CH_(3)` ` square ` Removal of H-atom from any of C-atom GIVES four different carbocations . (i) ` CH_(3) - underset(CH_(3))underset(|) overset (BETA)(CH)-overset(oo)(CH_(2) )- overset(+)(CH_(2))` (ii) ` CH_(3) - underset(CH_(3))underset(|) (CH)-overset(+)(CH_(2) )- CH_(3)` (iii) ` CH_(3) - underset(CH_(3))underset(|) overset(+)(C)larrCH_(2) - CH_(3)` (iv)` overset(+)(CH_(2)) - underset(CH_(3))underset(|) (C)- CH_(2) - CH_(3)` ` square ` Stability order of carbocation is ` 3^(@) gt 2^(@) gt 1^(@)` ` square ` Though I & IV are primary carbocations , I has ` alpha-CH_(3) ` group at ` beta `- carbon and while IV has ` - CH_(3)" at " alpha ` - carbon . ` square+ I ` EFFECT decreases with distance , hence IV is more stable than I ` squaretherefore `The overall stability is ` I lt IV lt II lt III `. |
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