RX Flashcards
(23 cards)
How does the BP of RX compare to R and why ?
BP of RX is higher than R
- C-X bonds are polar due to diff ENE, hence there is pd-pd interactions between RX molecules (stronger than id-id in R)
- There are more electrons presnetrs hence id-id intereaction are more extensive)
Why is RX insoluble in water ?
C-X bond is unable to form H bond with H2O
What makes RX reactive
C-X bond is polar and due to diff in ENE
C have partial positive charge and is electron deficient
Hence can attract nucleophile
How is RX prepared ?
- E addition of HX to alkene
- Nu substitution of alcohol
Describe E addition of HX to alkene to form RX
1. r&c
2. Mechanism
- HX(g)
2.
Describe Nu substitution of alcohol to form RX
1. r&c
2. Mechanism
- PCl5 r.t.p
- RX + POCl3 + HCl (g)
- PCl3, heat
- RX + H3PO3
- SOCl2, heat
- RX + SO2 + HCl (g)
- Dry HX(g) , heat
- RX + H2O
What are the
1. types of reactions that RX can undergo
2. products they form
- Elimination — alkene (opposite of E addition)
- Nu substitution — alcohol (opposite of Nu sub of alcohol)
- Nu substitution — nitrite
- Nu substitution — amine
Nu sub to alcohol
1. r&c
2. Mechanism
1.NaOH(an), heat
- Nu: OH-
How does Nu substitution to alcohol work for germinal-dihalides / trihalides
Carboxylic acid + H2O
Nu sub to nitrile
1. r&c
2. Mechanism
- KCN in ethanol
- Nu: CN-
Nu sub to amine
1. r&c
2. Mechanism
- Excess conc NH3 in ethanol, heat in a sealed tube
- Nu: NH3
Explain the r&c for Nu sub to amine
Conc:
1. NH3 wil dissociate to form NH4+ if its NH3(aq)
2. H2O is also a Nu and will act as the Nu if NH3(aq) forming alcohol instead
Sealed tube:
NH2 is a gas and will escape
What direction do electrons always flow ?
Nu to E
When does RX undergo Sn2 ?
Primary or secondary RX
What is the trend in Reactivity of RX and why ?
RI > RBr > RCl
Why:
Larger X, more diffused orbital, less effective overlap
C-X bonds is weaker and more easily broken
When does RX undergo
1. Sn1
2. Sn2
- Sn1
- tertiary RX
- steric hindrance - Sn2
- perimary and secondary RX
Why is a racemic mixture formed in Sn1 mechanism ?
There is 50:50 of each enantiomer because the Nu has equal chance of attacking the C+ intermediate form both sides since it is triganol planar about the C+
Will there always be a raemic mixture in Sn1 ?
No.
Only if the C+ is chiral, i not there is only 1 product
Describe Sn1 mechanism
Describe Sn2 mechanism
Describe elimination of RX
1. r&c
2. Mechanism
- KOH in ethanol heat
2.
What effect does strong base have on RX ?
RX — Alkene
Bcuz stronger base will steal H
What hints does reduction and hydrolysis give ?
Both reactions are step up or down reactions, hence no of C should remain the same
