[理學(xué)]第一章取代基效應(yīng)(完整版)
【正文】 H HC H 3HHC H 3C H 3H 3 COOC H 3OOH 3 CHHHHHHHHH HHHHHC H 3HC H 3HHHC H 3C H 3HH kJ/mol higher kJ/mol higher C H 3H3 CO HN O 2O HC H 3H 3 CN O 2p K a = 7 . 1 6 p K a = 8 . 2 42. 空間效應(yīng)對質(zhì)子酸 酸性的影響 CC H3C H3C H3CO HOCO HOpKao pKap 當(dāng) tButyl 在鄰位時， 把羧基擠出了與苯環(huán)所在 平面，苯環(huán)的 ＋ C效應(yīng)消失， I 效應(yīng)仍在 。 Collectively these Lewis diagrams are then known as resonance structures. 二 .共軛體系與共軛效應(yīng) Resonance effects (conjugation effects) Resonance effects are those that occur through the π system and can be represented by resonance structures. These can be either electron donating (. OCH3) where π electrons are pushed toward the group or electron withdrawing (. C=O) where π electrons are drawn away from the group. C C C C C C C N C C COHC C C C C C、 π π 共軛 體系 C1 C2 C3 C4 、 p π 共軛 體系 C3 C2 C1 CH3 H H + H C l C H C H 2 R COO HC H 3 C H C H C H 共軛效應(yīng)特點： 共軛效應(yīng)受距離的影響較小 C HY C H C H C H 2δδ δδ、 結(jié)構(gòu)特征：單、重鍵交替， 共軛體系中所有原子共平面 Y為吸電基－吸電子共軛效應(yīng) (C), X為供電基－供電子共軛效應(yīng) (+C). C C C Y XC C( I ) ( I I )O Hδδδ苯酚分子中氧原子上的孤對電子與 苯環(huán)上的 π電子形成 p π共軛。 電負(fù)性差值越大，強(qiáng)度越高； 距離越大，強(qiáng)度越弱。 Electrons in σ bonds have a fixed location and so they are said to be localized. ON R2N H2O HO RN H C O RRP hC H = C R2HO C O RA c t i v a t i n gE D GS t r o n g l y A c t i v a t i n gM o d e r a t e l y A c t i v i t i n gW e a k l y A c t i v a t i n gR e f e r e n c eo r t h o / p a r a d i r e c t i n gXC H OC O RC O O RC O O HC O C lC F3C NS O3HN+R3N O2D e a c t i v a t i n gE W GS t r o n g l y D e a c t i v a t i n gM o
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