aqueous KOH vs. alcoholic KOH

Water is a more polar solvent than alcohol. When water is used as the solvent, OH- ion undergoes hydration (i.e OH- ion is surrounded by water molecule due to the attractions between the OH- anion and the positive ends of the more polar water molecules) to a greater extent. This would sharply decrease the basic strength (the strength of accepting a proton) of the OH- ion. Therefore, elimination is less favorable.

When alcohol is used as the solvent, OH- ion undergoes salvation (i.e. OH- ion is surrounded by solvent (alcohol) molecules due to the attractions between the OH- anion and the positive ends of the less polar solvent molecules) to a smaller extent. This would not much decrease the basic strength of the OH- ion. Therefore, elimination is more favorable.

001 答案都好亂呢姐。

一個普通勁既 base，點會夠力去搶走人地既 H^+ 出來，變隻好勁既 base。隻好勁既 base 點解會咁禮讓，唔搶番個 H^+ 番呢。

即係話，你話 OH^- 搶走左 CH3CH2OH 個 H^+，變左個勁 base CH3CH2O^- 出呢。咁冇可能格，CH3CH2O^- 咁勁，一定會搶番個 H^+ 走，變番 CH3CH2OH。所以，一個有咁勁既 base，一定唔會變個勁過佢既 base 出呢既！

2008-03-08 18:00:12 補充：
睇清楚 001 個答案，OH^- 唔鬼係個 group，用 covalent bond 黐上個 molecule 度先叫做 group，伶伶仃仃一個帶負 charge 既粒粒叫做 ion。

KOH 有ge 係OH- group
一隻算係moderate ge base

alc. KOH
例如 KOH dissolve in ethanol
就出一隻stronger base , CH3CH2O-

RO- 係勁過OH- GE
因為stronger base favours elimination
weak base favours substitution.