Organic Chem, leaving groups, Nu:, E+

Question 1

What makes a good leaving group?

Answer 1

• Highly EN, attract electrons which polarises bond, making it weaker and easier to break. (halogens)
• Conj bases of strong acids
• BIG atoms, bigger, better good leaving group.
  so the smaller the atom is, the worse it is.
  I > Br > Cl > F

Question 2

What makes a good electrophile?

Answer 2

The more positive, the more liekly it is to attract electrons.

Question 3

What makes a good nucleophile?

Answer 3

• Small mass, allows it to not be sterically hindered so badly.

Question 4

What makes reaction SN1?

Answer 4

Rate of reaction = k*[C-X]
1 thing happening at a time.
Based on leaving group leaving first, therefore requires good leaving group.

Then any free Nu: immediately joins, likely to be most abudant nucleotide.

Transition stage is trigonal planar, so chirality is 50:50

Question 5

What makes reaction SN2?

Answer 5

Rate of reaction = k*
[C-X][Nu]
2 things happening at a time.
Based on leaving group leaving and nucleophile joining.
Backwards attack, reaction inverts chirality.

Question 6

What is an elimination reaction?

Answer 6

Nu: is a base which attracts a H to itself.
Leaving group is very stable on its own.
So form HNu: and L-

All based on strength of Nu: to pull protons to itself.
Strong bases: Tend to favour E2
Size: Bigger it is, worse Nu:

Question 7

What makes reaction E1?

Answer 7

Based on rate = k[C-L]
With SN1 get E1
More likely weak base, can be strong base
Weaker Nu:
Needs strong H bond solvent. If water, probs E1

Nu: attacks H, trying to pull it off.
Determining slow step is how slow it can pull it off.

Likely tertiary haloalkide.

Question 8

What makes reaction E2?

Answer 8

Based on rate = k[C-L][Nu:]
With E2 get SN2
Strong bases: Tend to favour E2
Weak bases: Can’t be E2
Strong Nu:
H bonding solvent gets in way of bonding.

Little sterical hinderance as H+ is easily accessible.
Difference of primary, 2ndry, 3try isn’t much.

Question 9

What is addition reaction?

Answer 9

ENu: attacks to break weakest bond and join, weakest bond is like pi/double bond.

Addition to either side of double bond, which breaks C=C and makes 2 new bonds.

Question 10

Steps of addition reaction

Answer 10

1: electrophile breaks bonds by attracting electrons

2: Nu: attacks carbocation

Question 11

What makes reaction fast addition?

Question 12

What makes reaction slow addition?

Question 13

What does aqueous NaOH mean?

Answer 13

Basically means lotsa salt dissolved in water

Question 14

In SN1 reaction, if there’s equal amounts of NaOH and H2O as a Nu:, which will become the nucleotide?

Answer 14

The NaOH is an anion, so it’ll act as the stronger nucleotide to the positive carbocation.

Question 15

In SN1, if H2O is more abudant than NaOH, which one will be nucleotide?

Answer 15

H2O.
It blocks the NaOH sterically, and due to its charge.
Then due to its abudance it become Nu:.

Question 16

What does chiral carbon mean?

Answer 16

4 diff groups attatched to 1 carbon

Question 17

What makes a reaction SN1 or SN2?

Answer 17

Structure, if it has 2-3 H’s it’s SN2
1 H could be SN1 or SN2
if it has 0 H’s its SN1

Question 18

If a reaction has 1 H attatched to a carbon, will reaction be SN2 or SN1?

Answer 18

Could be both

Question 19

If reaction has 0 H’s, is it SN2 or SN1?

Answer 19

SN1

Question 20

If reaction has 2 H’s is it SN2 or SN1?

Answer 20

SN2

Question 21

What stabilises? (in reference to electrons)

Answer 21

thing’s that donate electrons, nucleophiles.

Question 22

What destabilises? (in reference to electrons)

Answer 22

Things that accept electrons, such as electrophiles.

Question 23

What makes SN2 slower?

Answer 23

If it’s sterically hindered, meaning it’ll be harder for Nu: to backside attack, knocking off leaving group and attatching itself.

Easier done if groups are small or if there’s nothing there.

Question 24

What does SN1 require?

Answer 24

Good leaving group, as it is the rate determining step that begins the reaction.

Question 25

Why does atom size change how good of a leaving group it is?

Answer 25

Small atoms have shorter bonds which are stronger, meaning it’s less likely to break.
Leaving groups want this bond to break.

Question 26

What does protonation do to weak leaving groups?

Answer 26

Turns it into better leaving groups, by protonating them.

Question 27

What contributes to reactivity of a nucelophilic acyl substitution?

Answer 27

• Electronegativity..
  Larger pos charge on carbonyl carbon = more reactive
  Stability of the leaving group
  Nucleophility of the nucleophile

Question 28

What’s order of reactivity of an Nucleophilic Acyl substitution?

Answer 28

Acid chlorides and Anhydrides
- Then esters (requires acid catalysed reaction)
-Then C. Acid’s
- Then amides (bc. they are least electrophilic)

Question 29

What’s required for an amide to react in an Nucleophilic Acyl Substitution react?

Answer 29

• A strong base w/ heat
• Acid catalysed w/ heat

Question 30

Do solvents matter in SN1 and SN2?

Answer 30

Solvents able to form H bonds matter.
- SN1 more likely to occur, as this reaction proceeds w/ most abudent nucleophile. (H2O)
- SN2 less likely to happen, Anions Nu:’s are often sorrounded by H2O’s which prevent them from backside attacking. This makes Nu: worse. And SN2 requires good Nu: in order to knock off leaving group.

Question 31

What are phospholipids?

Answer 31

C. Acid derived esters, where a phosphate is also present.

Ionised phosphate may form a polar head, which helps in stabilising, that reduces ester breakdown.

Question 32

What are lipases?

Answer 32

Enzymes in our bodies that break down fatty acids (triglycerides)

Question 33

How do alkyls stabiilise carbons?

Answer 33

1 alkyl attatched - primary is less stable than 2 alkyls attatched - secondary. as more alkyls help to share charge and bonds which stabilises carbons.