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Flashcards in Block 4 Deck (48):
1

Alkenes are saturated/unsaturated

Unsaturated

2

Preparation of alkenes

Usually via elimination reactions

3

Reagent for dehydration (removal of H2O) alcohol (prep of alkene)

conc. H2SO4

4

Reagent for dehydrohalogenation (removal of HX) from alkyl halide (prep of alkene)

KOH or NaOH

5

When is the Saytzeff's rule used

In preparation reactions, when more than one alkene can be formed

6

Saytzeff Rule

The major product is the most substituted alkene, the one with the least number of H's directly attached to the C=C

7

Reagent for hydrogenation/reduction (alkene reaction)

H2/catalyst (e.g. Pt)

8

What does hydrogenation occur with?

Syn (same side)/cis

9

What does halogenation occur with?

Trans (diff sides)/anti because Br/Cl are "big atoms"

10

Reagent for halogenation (addition of electrophile E+)

Br2, Cl2

11

When is Markownikoff's rule used?

For addition reactions

12

What is Markownikoff's rule?

Addition of unsymmetrical reagent to unsymmetrical alkene. The C with the most amount of H's directly attached to it

13

Preparation of alkynes

Via didehydrohalogenation of dihaloalkanes

14

Reagent of didehydrohalogenation (for alkynes)

KOH or NaOH in ethanol

15

What reactions do alkynes undergo

Addition (same as alkenes)

16

Reagent for hydration (addition of H2O for alkynes)

H2SO4/HgSO4

17

What reaction do benzene and substitutued benzene undergo?

Usually substitution (because of resonance which prevents them from undergoing addition reaction)

18

Wheland intermediates

The resonance stabilised carbocation

19

Steps for preparation of monosubstituted benzenes

1. Generation of electrophiles
2. Electrophillic attack
3. Loss of proton H+

20

Generation of electrophiles

Usually formed by catalytic action.
Halogenation: Cl-Cl
Nitration: HNO3

21

Ortho-para strongly activating

-OH, -OR, -NH2, -NR2, NHR

22

Ortho-para weakly activating

-CH3

23

Ortho-para deactivating

-X (Cl, F, B, I)

24

Racemix mixture

Equal amounts of S and R (50:50)

25

Preparation of alkyl halides (haloalkane)

Addition (Markownikoff's rule applies)

26

Reagent for 1° and 2° alkyl halides

SOCl2

27

Reagent for 3° alkyl halides

HCl

28

Halogens are good leaving groups (as they are strong acids and weak bases. E.g.

1. I
2. Br
3. Cl

29

Poor leaving groups are

H-, NH2, HO-, RO-

30

What is a carbocation

A molecule that has a C atom bearing 3 bonds (instead of 4) and one positive charge

31

SN1 unimolecular mechanism is for:

3° alkyl halide (with one species involved)
It is substitution by a nucleophile (which reacts after r.d.s), one species is involved in the r.d.s

32

SN2 bimolecular mechanism for:

1° and some 2° alkyl halides (with two species involved)
Substitution by a nucleophile, two species involved in the r.d.s
no intermediates

33

Alkyl halides undergo what type of reaction

Elimination (from an alkyl halide to an alkene)

34

What reactions do alkenes undergo?

Addition (electron rich)

35

What is the product for all alkynes except ethyne?

Ketone

36

Meta directors strongly deactivating

NO2

37

Meta directors moderately deactivating

CHO2, COR, C---N

38

Meta directors are ....

very good electron withdrawing groups

39

How many resonance contributors for ortho-para substitution?

4 resonance contributors

40

How many resonance contributors for meta substitution?

3 resonance contributors

41

Which are excellent leaving groups?

I-, Br-, Cl- (weak bases)

42

Which are poor leaving groups?

H-, NH2-, HO-, RO-

43

Factors making Sn1 mechanism react faster?

stability (3° is more stable)
leaving group (I- is the best)

44

E1 unimolecular mechanism is for:

1° and 2°
Proceeds via carbocation intermediate,

45

What favours elimination over substitution? (3)

Stronger bases, higher temperatures, and non-nucleophilic solvent

46

E2 bimolecular mechanism is for:


Proton is removed, C=C is formed, C-X is broken all in a single (concerted) step

47

Vinyl halides can undergo .....

elimination with strong bases to form an alkyne

48

Alkyl halids and aryl halides form

Grignard reagents on treatment with Mg