Block 4; Functional Group Chemistry Flashcards
What are ortho/para directors that are strongly activating?
- OH
- OR
- NH2
- NR2
What are ortho/para weakly activating directors?
CH3- alkyl
What are ortho/para deactivating directors?
-X (F, Cl, Br, I)
What do oxygen, nitrogen and halogens all have in common?
Unshared electron pairs that can be donated into the aromatic rings (by resonance)
What are strongly deactivating meta directors?
NO2
What are moderately deactivating meta directors?
Aldehydes, ketones, nitriles
What do all meta directors have in common?
They have a multiple bind to the atom that is bonded to the aromatic ring sp2 carbon
What do activating directors do?
Speed up reactions
What do deactivating directors do?
Slow down reactions
What does the favoured ortho/meta substitution have?
More resonance contributors
What forms a race mic mixture of 50:50 S and R?
If an alkyl halide with a chiral centre is prepared
What are good leaving groups (weak bases)?
Cl
Br
I
What are poor leaving groups (strong bases)?
H, NH2-, HO-, RO-
What are the two mechanisms of alkyl halide substitution?
Sn1 unimolecular mechanism
Sn2 bimolecular mechanisms
What types of alkyl halide is Sn1 favoured for?
3 (tertiary), (some secondary and benzylic halide) where intermediate carbonation from breaking the c-x bond is relatively stable
Describe an SN1 reaction?
A substitution, by a nucleophile, where only one species in involved in the rate determining step (where the leaving group departs)
Which enantiomer produces a racemic mixture in Sn1 substitution reactions for alkyl halides?
Both R and S
Which alkyl halide substitution reaction is a 2 energy profile?
Sn1 mechanism
What favours sn2 bimolecular mechanisms?
1 halides and some secondary halides
What mechanism is concerted/synchronous?
Sn2 bimolecular mechanisms
Describe SN2 reactions?
Substitution, by a nucleophile, with two species involved in the rate determining step
Is there an intermediate carbonation in sn2 mechanisms?
No
What happens when a chiral non-racemic secondary halide reacts via a Sn2 pathway?
A chiral, non-racemic (optically active) product results from the inversion of configuration
Why is a primary halide favoured for SN2 reactions?
Because it’s not too crowded to have the transition state (body does Sn2 Chem)
Two types of alkyl halide elimination reactions?
E1 unimolecular
E2 bimolecular
What does E1 mechanisms favour?
Tertiary
What happens if Sn1 and E1 compete?
Product mixtures are produced
Does the zaitsev rule apply to E1 mechanisms?
Yes, where more than one Alkene can be formed
What favours Elimination (E) over Sn (substitution)?
Stronger bases, higher temperatures and a non-nucleophilic solvent
What are E2 mechanisms?
When the proton is removed (C=C bond formed), and the C-X bond is broken, all in a single concerted step
What does E2 reactions require?
A strong base
What do E2 reactions favour?
Tertiary
When can E2 be observed in primary halides?
If product extends conjugation
Examples of a weak nucleophilic neutral reagent?
H20, CH3OH, CH3CH2OH
What are stronger nucleophiles with low basicity?
Cl, Br, I, CN-, CH3S-, CH3COO-
What are stronger nucleophile, high basicity reagents?
HO-, CH3O-, CH3CH2O-, H3N, (CH3)3N, H2N
Describe the reactions of alkyl halides 1,2,3 for weak nucleophile, neutral reagents?
Primary; SN2
Secondary; SN1 or SN2
Tertiary; Sn1 and E1
Describe the alkyl halide reaction for 1,2,3 with a stronger nucleophile, low basicity reagent
Primary; SN2
Secondary; Sn2
Tertiary; Sn1 and E1
Describe the alkyl halide of a stronger nucleophile, high basicity reagent for 1,2,3
Primary; Sn2
Secondary; Sn2 and E2
Tertiary; E 2
What is a Holden attached to a sp2 carbon not susceptible to?
SN (so no reaction)
What can Grignard reagents act as?
Carbon nucleophile
What reagent is used in the catalytic dehydrogenation of alkanes (to alkenes)?
Pt/Pd, heat at 600C
What reagent is used in the acid-catalysed dehydration of (removal of H2O from) alcohols? (To form alkene)
Concentrated H2SO4
What reagent is used in the base promoted dehydrogenation of (removal of HX from) alkyl halides (to form alkene)?
KOH or NaOH
What type of preparations usually form alkenes?
Elimination
What reagent is used in the hydrogenation of alkenes?
H2/catalyst (e.g Pt)
What stereochemistry does the hydrogenation of alkenes involve?
Syn
What reagent does the halogenation of alkenes involve?
Br2, Cl2
What sort of stereochemistry does the halogenation of alkenes occur in?
Anti-stereochemistry (trans)
Which is more stable; secondary or primary carbocation?
Secondary
