Halogenoalkanes and aromatics Flashcards
Nomenclature of halogen alkanes
- The halogen and o e.g. floro, bromo
- Location and number must be specified e.g. di, tri, tetra
What intermolecular forces do halogenalkanes have
- Due to the high electronegativity of the halogen atom it will attract electrons making it slightly negative and the carbon will be slightly positive.
- They have a permanent dipole so have permanent dipole-permanent dipole interactions
What is a chloroflourocarbon
- Halogenalkene with all the hydrogens relaced by flourene or chlorine
- CFC’s are damaging to the ozone layer
Whats homolytic fission
The breaking of a covalent bond such that both atoms have an unpaired electron
Initiation of chlorine
Uv light breaks the bond between a Cl2 molecule to produce 2 chlorine free radicals
Propogation of Cl
The reaction of any particals that produces a free radical so the reactions can keep occuring
Termination of Cl
Any reaction that doesnt form a free radical such as 2 free radicals coming together or 2 carbons bonding
Whats a nucleophile
A chemical species that donates an electron pair to an electron deficient centre
Nucleophilic substitution (SN2)
- The nucleophile attacks the electron deficient carbon atom
- An intermediate with both atoms bonded is formed
- The bond between the carbon and halogen breaks giving the halogen the electrons
Nucleophilic substitution (SN1)
- The bond to the halogen breaks
- A carbonium ion intermediate is formed
- The nucleophile attacks the carbon
How to test for halide ions
- The halogenalkane must be hydrolysed by boiling it in sodium hydroxide
- It is acified with dilute nitric acid
- Aqueous silver nitrate is added
- A precipitate is formed
- If chloride is its white, bromide is cream and iodide is yellow
Elimination of halogenalkanes
- High temp without air
- In the presence of a strong base
- The halogen accepts the electrons breaking the bond between it and the carbon
- The electrons between carbon and hydrogen then form a C=C and the base accepts the proton given off
- Whats produced is an alkene, Base-H and lone halogen atom
Whats a leaving group
- An atom that can accept electrons and leave a molecule
- Often a halogen
- A good leaving group has a high electronegativity
What is an aromatic compound
Any compound that contains atleast one benzene ring
Describe the bonding in a benzene ring
- Sigma bonds between carbons
- Pi bonds above and below due to P-orbitals
- Rings of 6 delocalised electrons above and below the ring
Nomenclature of aromatic compounds
- Carbon number 1 is wherever the other molecule is attached
- OH = phenol, always on carbon 1
- Alphabetical order
Nomenclature of aromatic compounds
- Carbon number 1 is wherever the other molecule is attached
- OH = phenol, always on carbon 1
- Alphabetical order
Mechanism of chlorination of benzene
- AlCl3 accepts a pair of electrons from Cl2 to generate a Cl+ electrophile
- Electrons from the benzene ring go to the cl+ forming a bond, the ring will have a u+ inside
- The H-C bond is broken giving the electrons to the ring
- A H+ is produced
Mechanism of Friedel-Crafts alkylation
- An electrophile (CH3+) is generated by reacting CH3Cl with AlCl3
- Electrons from the inner ring are transfered to the akyl group forming a bond
- The ring becomes a u+
- The C-H next to the akyl group is broken and the electrons are transfered to the ring
- The H+ is released as a product
Acylation of benzene
The same as chlorinaton and akylation but with COCH3
Substituent effects on benzene
- Alkyls are activating
- Halogens are deactivating
- NO2 is deactivating
- OH is activating
- Activation occurs when electron density is increased
General mechanism for electrophilic substitution to phenol and phenylamine
The reactants bond to the 2, 4 and 6 carbons and 3 hydrogens are produced
Reaction of phenol with sodium
- Na replaces the H in the alcohol to form a O-Na+
- hydrogen gas is a product
Why can phenol act as a nucleophile
- Theres a lone pair on the O
