Hard / soft nucleophiles

Question 1

two main types of interactions that affect a reaction

Answer 1

electrostatic effects
HOMO-LUMO interactions

Question 2

large nucleophiles energy of lone pairs

Answer 2

high energy lone pairs - high HOMO, because they have many e-s

Question 3

charge for large nucleophiles

Answer 3

often uncharged
if charged, charge is spread diffusely over large orbitals

Question 4

reaction of large nucleophiles with C=O groups

Answer 4

reacts very poorly at C=O groups, but quickly with saturated C

Question 5

are large nucleophiles HARD or SOFT nucleophiles?

Answer 5

SOFT
think large and fluffy

Question 6

what’s the dominant interaction for large nucleophiles?

Answer 6

HOMO-LUMO dominated rather than electrostatics

because high HOMO –> small HOMO-LUMO gap
and low charge density / often uncharged means electrostatics unimportant

Question 7

reaction of small nucleophiles (eg. OH-) with C=O groups

Answer 7

attacks the C=O rapidly

Question 8

electrons in small nucleophiles

Answer 8

concentrated close to the (often electronegative) nucleus, very localised

ie. low HOMO

Question 9

charge density in small nucleophiles

Answer 9

charged and small hence high charge density

Question 10

are small nucleophiles HARD or SOFT?

Answer 10

HARD nucleophiles
with a low HOMO

Question 11

dominant interaction for reactions with hard nucleophiles

Answer 11

low HOMO –> large HOMO-LUMO gap hence cannot be dominated by FMO interactions

high charge density –> electrostatics-driven, but orbitals are still used for the reaction to occur

Question 12

hard / soft nucleophiles basicity

Answer 12

HARD nucleophile X = basic (HX = weak acid)
SOFT nucleophile Y = not basic (HY = strong acid)

Question 13

examples of hard nucleophiles

Answer 13

RO-
NH2-
MeLi

Question 14

examples of soft nucleophiles

Answer 14

RS-
I-
R3P