Functional Groups

Question 1

Why are alkanes known as paraffins ?

Answer 1

• due to unreactivity

Question 2

What state are alkanes ?

Answer 2

• CH4 to C4H10 are gases
• C5H12 to C17H36 are liquids
• C18H38 and above are solids

Question 3

Why does bp of Alkanes increase as chain length increases ?

Answer 3

• More London forces
• more surface points of contact

Question 4

what is an electrophile ?

Answer 4

• electron lover
• accepts a pair of electrons

Question 5

what is a nucleophile ?

Answer 5

• donates a pair of electrons

Question 6

what is the HOMO?

Answer 6

• highest occupied molecular orbital
• nucleophile has pair of e- in the HOMO

Question 7

what is the LUMO ?

Answer 7

• low energy anti-bonding orbitals
• lowest unoccupied molecular orbitals

Question 8

what does a curly arrow represent ?

Answer 8

• movement of a pair of electrons from a filled orbital into an empty one

Question 9

What is the difference between SN1 and SN2 mechanisms ?

Answer 9

• SN1 - leaving group goes first , carbocation produced and then nucleophile attacks
• SN2 - nucleophile attacks same time as leaving group goes so no carbocation

Question 10

what 3 things does rate of an Sn2 reaction depend on ?

Answer 10

• nucleophile
• carbon skeleton
• the leaving group

also temp + solvent

Question 11

what 2 factors does rate of Sn1 reaction depend on ?

Answer 11

• carbon skeleton
• the leaving group

temp + solvent

Question 12

what is the RDS (rate-determining step) in Sn1?

Answer 12

• formation of carbocation

Question 13

How does structure of carbon skeleton affect Sn1 reaction ?

Answer 13

methyl + 1°= no cause unstable carbocation
2° = moderate, slower than 3°
3° = fastest very stable cation

Question 14

How does structure of carbon skeleton affect Sn2 reaction ?

Answer 14

methyl + 1°= fastest due to low steric hindrance
2° = moderate some steric hindrance
3° = no, high steric hindrance

Question 15

what is steric hinderance ?

Answer 15

• slowing down of a chemical reaction due to bulk of other groups

Question 16

How does steric hinderance affect Sn1 reactions ?

Answer 16

• stabilises carbocation

Question 17

how does steric hinderance affect Sn2 reactions ?

Answer 17

• low steric hinderance easy for nucleophile to attack

Question 18

what is a racemic mixture and how does it form in Sn1 reactions ?

Answer 18

Racemic -contains equal amounts of 2 enantiomers.
- in sn1 - when a chiral carbon forms a carbocation , nucleophile can attack from both sides

Question 19

what is a polar protic solvent ?

Answer 19

• can form H bonds
  eg. water, alcohol

Question 20

what is an aprotic solvent ?

Answer 20

• cannot form H bonds

Question 21

does sn1 take place in protic or aprotic solvents ?

Answer 21

• protic because they stabilise carbocation

Question 22

does sn2 take place in protic or aprotic solvents ?

Answer 22

• apotric

Question 23

how is the stereochemistry inverted in Sn2 ?

Answer 23

• nucleophile attacks from backside , side oppsodie to the one where leaving group goes

Question 24

Does the double bond in Alkenes act as a nucleophile or electrophile ?

Answer 24

• nucleophile

Question 25

How does conversion of alkene isomers occur ?

Answer 25

- breaking of pi bond - eg. cis to trans conversion

Question 26

What are the 2 methods of preparing alkenes ?

Answer 26

- cracking - elimination of halides/alcohols or

Question 27

how does cracking produce alkenes ?

Answer 27

- long chain alkanes are cracked to form a alkene and smaller alkane

Question 28

When does anti - markovinikov addition occur?

Answer 28

' Presence of peroxides

Question 29

What are alkynes?

Answer 29

- Contains triple c-c bonds - 2 pi and 1 sigma bond

Question 30

What is a stereospecific reaction ?

Answer 30

- stereochemistry of reactant determines stereochemistry of product

Question 31

what is a diastereoisomer ?

Answer 31

-non- mirror images

Question 32

what is the bromonium ion and is it an electrophile or nucleophile ?

Answer 32

- Br+ - electrophile

Question 33

What is the inductive effect ?

Answer 33

- electron withdrawing groups (electronegative ) pull e- towards themselves through sigma bond - electron donating groups (alkyl) push e- density onto positively charged center

Question 34

Why is tertiary carbocation more stable than primary ?

Answer 34

- greater number of alkyl groups - more carbons = increased positive inductive effect

Question 35

What conditions are needed for anti-markovnikovs rule ?

Answer 35

- peroxide - hydrogen bromide

Question 36

Difference between anti and normal markovnikovs?

Answer 36

- anti uses radicals not carbocations - in anti- H attaches to C with fewer H's - wheras in normal it attaches to one with most H's

Question 37

stages of anti-markovnikov addition

Answer 37

- initiation - RO–O–R→2RO* - propagation - RO*+HBr→ROH+Br* Br* adds to the less substituted carbon of the alkene, creates a new alkyl radical on the more substituted carbon of the alkene. termination = Br*+Br*→Br2 alkyl radical+Br*→bromoalkane

Question 38

conditions for hydrogenation of alkenes

Answer 38

- 150c - Ni,pt,pd (palladium) catalyst

Question 39

which hybridsation of carbon is more electronegative ?

Answer 39

sp>sp2>sp3

Question 40

what does tautomerisation of alkynes form ?

Answer 40

alkyne ---> enol ----> ketone

Question 41

what is an enol ?

Answer 41

- alkene with an OH group

Question 42

How are haloalkanes prepared ?

Answer 42

- radical substitution of alkanes - halogenation of alcohols - electrophilic addition of alkenes

Question 43

What happens to acidity as alkyl group increases (positive inductive effect)?

Answer 43

- Acidity decreases as alkyl group increases

Question 44

What effect does negative inductive effect have on acidity ?

Answer 44

- increased acidity

Question 45

What are 3 methods of preparing alcohols ?

Answer 45

- hydration of alkenes - reduction of aldehydes and ketones - hydrolysis of haloalkanes

Question 46

reduction of aldehydes and ketones ?

Answer 46

- reduced by NaBH4 or LiAlH4 - acts as H- source - aldehydes reduced to 1° alcohol - ketone reduced to 2° alcohol

Question 47

what is an alkoxide ion and how is it formed ?

Answer 47

- deprotination of OH - R−O-

Question 48

how are esters formed ?

Answer 48

- carboxylic acid + alcohol -----> ester - in presence of acid catalyst

Question 49

oxidation of alcohols ?

Answer 49

- 1° alcohol --> aldehyde --> carboxyllic acid - acidified potassium dichromate - 2° alcohol - ketone

Question 50

what is the role of alcohol dehydrogenase ?

Answer 50

- converts alcohol to aldehyde

Question 51

what is the aldehyde dehydrogenase ?

Answer 51

- converts aldehyde to carboxyllic acid

Question 52

what is the shape and hybridisation of phenol ?

Answer 52

- sp2 - planar

Question 53

is phenol more acidic than alcohols ?

Answer 53

- yes because the phenoxide ion is stabilised by resonance

Question 54

what is the role of the hormone epinephrine ?

Answer 54

- fight or flight response

Question 55

what are primary, secondary, tertiary, amines ?

Answer 55

- primary - 2H - secondary - H - tertiary - no H's

Question 56

why are amine salts more soluble compared to amines ?

Answer 56

- amine salts are ionic - eg. NH3+Cl-

Question 57

Is a H bond in alcohol or amine stronger

Answer 57

- alcohol because O is more electronegative

Question 58

What is a zwitterion ?

Answer 58

- formed from amino acids - have a NH3+ group and COO- group - have a pH of 7

Question 59

how are nitriles formed ?

Answer 59

- Alkyl halide + NaCN

Question 60

how are amides formed ?

Answer 60

- Carboxyllic acid + SOCl2 + NH3

Question 61

how are amides formed from amines ?

Answer 61

- Acid chloride (RCOCl) + 1 or 2 Amine

Question 62

how are sulfonamides made?

Answer 62

- Sulfonyl chloride (R-SO₂Cl) and 1 or 2 amine