U3S2 halogenoalkanes Flashcards
1
Q
What is a halogenoalkane
A
- alkane with at least one halogen atom in place of a hydrogen atom
2
Q
Why are halogenoalkanes polar
A
- halogens are generally much more electronegative than carbon
3
Q
What is a nucleophile
A
- electron-pair donor
- attracted to an atom without enough electrons
4
Q
Conditions of halogenoalkanes and OH-
A
- nucleophilic substitution
- warm
- aqueous sodium or potassium hydroxide
5
Q
Steps for halogenoalkanes and OH-
A
- C-Br bond is polar so C+ attracts lone pair of electrons from OH-
- OH- ion acts as a nucleophile, attacking the slightly positive carbon atom
- New bond forms between C and OH- ion, making alcohol
- C-Br bond breaks and both electrons from bond are taken by Br
6
Q
Conditions for halogenoalkanes and CN-
A
- nucleophilic substitution
- warm
- ethanolic potassium cyanide
7
Q
Conditions for halogenoalkanes and NH3
A
- nucleophilic substitution
- warm
- excess ethanolic ammonia
8
Q
Steps for halogenoalkanes and NH3
A
- Nitrogen atom donates its lone pair of electrons to carbon atom to create a bond
- Nitrogen atom was neutral to begin with so is left with a positive charge
- Second ammonia molecule removes a hydrogen from NH3 group to form an ammonium ion and an amine
- Ammonia molecule donates its lone pair of electrons to hydrogen to form a bond, so nitrogen in ammonium atom has a positive charge and amine has no charge
9
Q
Reactivity of halogenoalkanes
A
- increases down group 7
- bond strength decreases
10
Q
Steps of a nucleophilic substitution reaction
A
- Lone pair of electrons on nucleophile attacks slightly positive charge on carbon
- Lone pair of electrons creates a new bond between the nucleophile and the carbon
- Addition of nucleophile breaks bond of carbon and halogen
- Pair of electrons from carbon-halogen bond are taken by halogen and become a lone pair
