Chapter 7: Pi bonds as electrophiles

Question 1

electrophiles

Answer 1

• electron lovers
• a group ( or atom) that wants to accept electrons
• this often comes from a deficiency of electron density on the group/atom

Question 2

nucleophiles

Answer 2

• nucleus lovers
• a nucleophiles is a group (or atom) that wants to donate electrons
• this often comes from an excess of electron density on the group/atom

Question 3

electrophilic

Answer 3

-carbon atom of the carbonly

Question 4

nucleophilic

Answer 4

• oxygen atom of the carbonyl

Question 5

which atoms are electrophilic in an alcohol? which atoms are nucleophilic

Answer 5

• as the entire molecule is neutral, it can react either as a nucleophile or an electrophile
• when the reaction involved only the exchange of a proton, the nucleophilie is called a base and the electrophile is an acid

Question 6

what happens if we deprotonate an alcohol (usinf base)?

Answer 6

• with more electron density on it the oxygen atom of the alkoxide is more nucleophilic
• as the entire molecule is negatively charged overall, it will most likely react as a nucleophile or a base
• it is unlikely to act as an electrophile or an acid because there is already excess electrons

Question 7

why is the N atom not attacked by a nucleophile

Answer 7

• it is very common for a positive charged atom to NOT be the atom that is attacked by a nucleophile
• the bond is broken adn electrons are pushed onto an N atom

Question 8

double and triple bonds

Answer 8

• when the positive charge is on an atom involved in a double triple bond, the nucleophile will attack the adjacent atom on the double or triple bond

Question 9

negative charge

Answer 9

• a negative charge is located on an atom bearing a lone pair of electrons, and that atom plays the role of the nucleophile (thanks to the lone pair
• the atom bearing a negative charge does not have alone pair of electrons, in this cases, the molecules can still react as nucleophile but it must use electrons from one of the bonds

Question 10

relationship to acid-base reactions

Answer 10

• the proton of the acid is an electrophile
• the basic atom of the base is a nucleophile
• acid-base reactions are usually much faster

Question 11

comparing nucleophiles

Answer 11

• nucleophilicity is directly proportional to basicity ( the same molecule can act as a base/neucleophile
• stronger the base - stronger the nucleophile
• weaker the base - weaker the nucleophile

Question 12

simple examples

Answer 12

• nucleophiles form new bonds by donating a pair of electrons to an electrophilic

Question 13

what if we use an alcohol instead of an alkoxide

Answer 13

you change the nucleophile

Question 14

hydride attacks

Answer 14

• the smallest nucleophile is hydride (H-)
  hydride on its own, sodium hydroxide (NaH) potassium hydride (KH) could at as a nucleotide
  but instead it almost always acts as a base
• this irreversibly forms hydrogen gas (H-H)
• if we want nucleophilic hydride we have to use a different hydride source
• the most common ones are [metalloid ] hydrides, usually borohydride (BH4) of aluminum hydride (AlH4)

Question 15

aluminum hydrides

Answer 15

• because the Al-H bonds are much more polar than B-H bonds aluminum hydrides are much more reactive than borohydrides

Question 16

Work up or Quench

Answer 16

for both borohydride and aluminum hydride reactions, it is acceptable to just draw the mechanisms happening once

Question 17

oxidation states

Answer 17

• oxidation/ reduction reactions (sometimes redox reactions) are already familiar
• oxidation and reduction are more commoly associated with the loss or gains of hydrogens

Question 18

oxidation states H

Answer 18

of H bonds influences redox reactions, the more hydrogen the more reduced

Question 19

oxidation states O

Answer 19

adding O2 to products = oxidation
removing O2 from products = reduction