أقرأ أيضاً
التاريخ: 11-9-2019
833
التاريخ: 28-8-2019
1041
التاريخ: 2023-07-26
1285
التاريخ: 7-9-2019
659
|
There is a further aspect of polar additions to alkenes that we should consider, namely, that electrophilic reagents form loose complexes with the ππ electrons of the double bonds of alkenes prior to reaction by addition. Complexes of this type are called charge-transfer complexes (or π complexes). Formation of a complex between iodine and cyclohexene is demonstrated by the fact that iodine dissolves in cyclohexene to give a brown solution, whereas its solutions in cyclohexane are violet. The brown solution of iodine in cyclohexene slowly fades as addition occurs to give colorless trans-1,2-diiodocyclohexane.
Precise Lewis structures cannot be written for charge-transfer complexes, but they commonly are represented as
with the arrow denoting that electrons of the double bond are associated with the electrophile. These complexes probably represent the first stage in the formation of addition products by a sequence such as the following for bromine addition:
|
|
دراسة يابانية لتقليل مخاطر أمراض المواليد منخفضي الوزن
|
|
|
|
|
اكتشاف أكبر مرجان في العالم قبالة سواحل جزر سليمان
|
|
|
|
|
اتحاد كليات الطب الملكية البريطانية يشيد بالمستوى العلمي لطلبة جامعة العميد وبيئتها التعليمية
|
|
|