chapter 15 haloalkanes Flashcards
What is the prefix for a haloalkane
- chloro
- bromo
- iodo
Describe the polarity of haloalkanes
- haloalkanes have a carbon halogen bond in their structure
- halogen atoms are more electronegative than carbon atoms
- the electronegativity is closer to the halogen atom than the carbon atom in the bond
- the carbon halogen bond is polar
what is a nucleophile
- a species that donate a lone pair of electrons
What is the mechanism for when a nucleophile reacts with a halogen
nucleophillic substiution
Describe the other definition for a nucleophile
- is an atom or a group that is attraccted to an electron deficient carbon atom where it donates a pair of electrons to form a new covalent bond
give examples of nucleophiles
- hydroxide ions -OH -
- water molecles - H2O
- ammonia molecules NH3
What are the three different structures of haloalkanes
- primary
- secondary
- tertiary
Describe the cause of reactivity of the haloalkanes
- polarity of the carbon - halogen bond
- in haloalkanes the carbon atom has a slightly positive charge and it attract species containing a lone pair of electrons
Describe the nucleophillic substitution of haloalkanes in general
- primary haloalkanes undergo nucleophillic substitution reactions with a vaireyt of different nucleophiles to produce a wide range of different compounds
what is a substitution reaction
- where one atom or a group of atoms is replace by another atom or group of atoms
What qare hydrolysis reactions
- is a chemical reaction involvig water or an aqueous solution of hydroxide that causes the breaking of a bond in a molecule .
- results with two products
Describe the nucleophillic substiution of a haloalkane and an OH group
- the nucleophile OH - approaches the carbon atom attatched to the halogen on the opposite side of the molecule from the hydrogen atom
- this direction of attack by the OH - ion minimisses repulsion between the nucleophile and the negative dipole of the halogen atom
- a lone pair of electrons on the hydroxide ion is attracted and donated to the positive dipole on the carbon atom
- a new bond is formed betwen the oygen atom of the hydroxide ion and the carbon atom
- the carbon halogen bond breaks by heterolytic fission
- the new organic product is an alcohol and a halide ion is also formed
How can haloalkanes be converted in alcohols and descibe how to obtain a good yield of product
- using aqueous sodium hydroxxide.
- the reaction is very slow at room temperture so the mixture is heated under refluz
- this is a hydrolysis reaction
Describe the prediction made from the bond enthalpies of carbon halogen bonds
- iodoalkanes react faster than bromoalkanes
- bromoalkanes react faster than chloroalkane
- fluoroalkanes are unreactive as a large amount of energy is required to break C-F bond
Describe the rate of hydrolysis of haloalkanes based on bond enthalpies
- in hydrolysis the carbon halogen bond is borken and the Oh groups replacces the halogen in the haloalkane
- the rate of hydrolysis depends upon the strength of the carbon halogen bond
- C-F havine the strongest bond enthalpies therefore the react more slowly than C-I which has the weakest bond enthalpy and therefore react quicker
Describe how you can meaure the rate of hydrolysis of primary haloalkanes
- 1-chlorobutane, 1- bromobutane ,1- iodobutane - any alkane
- the rate of reaction can be followed by the prescene of aqueous silver nitrate as the reaction take place in halide ions are produced which react with silver ion to form a preciptiate of silver halide
- haloalkanes are insoluble in water and so reaction is carried out in prescence of ethanol solvent
- ethanol allows the water and the haloalkane to mi and produce a single solution rather than two layers
What is the nucleophile present in the hydrolysis of haloalkanes
- water present in aqueous silver nitrate
What is the observations of explained by the carbon - halogen bonds
- slowest rate of reaction is the one that has the stronget carbon - halogen bond
- 1-chlorobutane reacts slowest and the C-Cl bond is the strongest
- 1-iodobutane reacts fastest and the C-I bond is the weakest
- rate of hydrolysis increases as the strength of the carbon - halogen bond decreases
What are organohalogen
- are molecules that contain at least one halogen atom joined to a carbon chain
What can organohalogen be use for
- general solvent
- dry cleaning solvents
- making polymers
- flame retardants
- refrigerators
- pesticides
Where are organhalogen found and how they are broken down
- rarely found in nature but broken down naturally in the environment
What is UV-B radiation and why is it harmful
- radiation most commonly known for suburn
- increased genetic damage
- greater risk of skin cancer to humans
What occurs in the stratosphere
- ozone is continually being formed and broken down by UV radiation
- intially very high energy UV breaks oxygen molecules into oxygen radicals
- O2-2O
- O2 and oxygen radicals in which ozone forms and then break down
- O2+O->O3
What does CFCs stand for
chloroflourocarbons
What are CFCs and HCFCs used as
- refrigerants
- air conditioning units
- aerosol propellents
How are CFCs stable
- very stable because of the strength of the carbon - halogen bonds within their molecules
What are the three layers of the ozone layer
- ozone layer
- stratosphere
- troposphere
What is ozone
- is an allotrope for oxygen gas found natrually in the stratosphere
- ozone molecules and oxygen atoms exist iin equilibrium in the upper atmosphere
- O2+O-> O3
Describe the fromation and destruction of the ozone layer
- occur naturally in a delicate valance something else introduced in balance easily upset it
describe two major sources of NO radicals
- lightning
- aircraft engines
What do No radicals do
- important contributer to ozone depletion
What are advantages if CFCs
- compressible
- volatile
- non toxic : CH3CL, NH3, SO2
- non flammable
What plastics are made from haloalkanes
- PVC - polynvinylchloride
- PTFE - polytetraflurouethane
Describe initiation for the destruction of the ozone layer
- CFCs break down in prescence of UV light forming radicals
- CF2CL2->CF2Cl+CL
Describe propogation of destruction of the ozone layer
- chlroine radicals attack ozone forming oxygen molecule and chlorate radicals
- CL + O3-> CLO +O2
- chlroate radicals react with oxygen radicals forming oxygen molecule and chlroine radicals
- CLO + O ->O2 +CL
- O3 + O -> 2O2
What is nucleophillic substitution
- an atom or group with an electron pair is exchanged for another atom or group
- the atom or group causing the substitution is a nucelophile that donates an electron pair donor
