Nucleophile vs Electrophile

Nucleophile: is negative so is attracted to positive parts of molecules
has an electron pair it can donate
example reaction: (OH)-ion added to halogenoalkane, displacing halide ion to for alcohol. 

Electrophile: is positive so is attracted to negative parts of molecules, like a double bond (electron lover)
wants to accept an electron pair 
example reaction: Hydrogen bromide (H is delta +ve due to dipolar bond) added to alkene (with double bond) to form halogenoalkane. 


Answer to the ochem problem from earlier this week! The basic hydrolysis of the bottom ester is observed to run significantly faster than the top ester due to a phenomenon known as anchimeric assistance, or neighboring group participation. 

When the two groups are para to each other, hydrolysis proceeds as normal, with nucleophilic attack at the ester carbonyl and collapse of the tetrahedral intermediate to give the carboxylate and methanol. If the groups are ortho to each other, something completely different can happen.

Remember that aldehyde carbonyls are significantly more reactive than ester carbonyls. This means that hydroxide is actually more likely to attack the aldehyde to form a deprotonated gem-diol first (in fact, it’s also more likely with the para aldehyde, although that hydration goes nowhere really fast). At this point, you have a nucleophilic oxygen positioned right next to the ester. This increases the effective concentration of nucleophile in the vicinity of the ester (why worry about waiting for a hydroxide to come along and collide when you have an anionic oxygen right next to you?). This gives you a sort of lactone, which can also be broken open to give the final carboxylate.

Shoutout to autobahnvismarck for getting it right, and radioactivepigeons, oddchelonian, and bonbubs for making good attempts! :D