6.3 halogenoalkanes & alcohols Flashcards
name the prefixes of Cl, F, Br, I
chloro, fluoro, bromo, iodo
describe primary, secondary & tertiary halogenoalkanes / alcohols.
primary - at end of carbon chain
secondary - the bonded carbon is bonded to 2 other carbons
tertiary - the bonded carbon is bonded to 3 other carbons
what state is halogenoalkanes usually at?
colourless liquid
which 3 halogenoalkanes are gases at room temperature?
chloromethane, bromoethane, chloroethane
which will have a higher boiling point, the parent alkane or the halogenoalkane? explain why.
- halogenoalkane
- polarity of C-X bond leads to stronger intermolecular forces
describe the solubility of halogenoalkanes in water.
sparingly soluble, since dipole-dipole forces are much weaker than hydrogen bonding in water
how is halogenoalkanes prepared from alkanes?
- free-radical substitution under heat / UV light
- halogen atom replaces hydrogen atoms
how is halogenoalkanes prepared from alkenes?
- addition of hydrogen halide / halogen elements to form halogenoalkanes with 1/2 halogens
how is halogenoalkanes prepared from alcohols?
react with phosphorus/hydrogen halides
In which 4 ways could halogenoalkanes react by nucleophilic substitution?
- water
- hydroxide ions
- cyanide ions
- ammonia
what conditions are needed for the hydrolysis of halogenoalkanes with water? what is the result?
- with silver nitrate in ethanol
- forms silver halide (precipitate)
what conditions are needed for the nucleophilic substitution of halogenoalkanes with hydroxide ions?
- warm aqueous alkali
- under reflux
what conditions are needed for the nucleophilic substitution of halogenoalkanes with cyanide ions?
- warm ethanolic potassium cyanide
- under reflux
what is the prefix for cyanide compounds?
nitriles
what conditions are needed for the nucleophilic substitution of halogenoalkanes with ammonia?
excess ethanolic ammonia
heat under pressure in sealed tube
what are the product of ammonia reacted compounds?
(primary) amines
what are the products of elimination of halogenoalkanes with hydroxide ions?
- alkenes
- halide ion
- water
what are the conditions of elimination of halogenoalkanes with hydroxide ions?
- hot ethanolic alkali
describe the difference in boiling point of the alcohol and its parent alkane.
higher boiling point since the hydrogen bonding in -OH is stronger than London forces in alkanes
which 2 alcohols are liquids are room temperature?
ethanol & methanol
what does complete combustion of alcohols produce?
CO2 + H2O
what is a nucleophile?
species that donate a lone pair of e- to form a covalent bond with an electron-deficient atom
what does the hydroxide ion act as in an elimination reaction?
base
rank in order of time taken in terms of tertiary, secondary & primary halogenoalkanes during hydrolysis.
tertiary < secondary < primary
explain in terms of bond enthalpy the trend in reactivity of iodo-, bromo-, chloro- alkanes.
C-I bond has the weakest bond enthalpy so therefore breaks most easily.
what is formed in partial oxidation by acidified potassium dichromate of primary alcohols?
aldehyde + H2O
what is the general formula of an aldehyde?
R-CHO
what is formed in the full oxidation by acidified potassium dichromate of primary alcohols?
carboxylic acids
what is the general formula of a carboxylic acid?
R-COOH
what is the prefix name with an aldehyde?
-nal
what reagents are required in oxidation of primary alcohols?
[O] oxidising agent
what is removed from an alcohol that forms an aldehyde?
H from OH and another H that is attached to the same carbon
what is formed in the oxidation of secondary alcohols?
ketone
what is the prefix name of ketones?
-one
in aldehydes, carboxylic acids & ketones which 2 don’t require naming carbon chain positions?
carboxylic acids & aldehydes
what is formed in elimination of alcohols with concentrated phosphoric acid?
alkenes + H2O
what are the observations on reacting Na & alcohols?
- effervescence
- mixture gets hot
- sodium dissolves
- white ppt produced
how is chloroalkanes formed from alcohols?
PCl5 / PCl3 / conc. HCl / mixture of NaCl + H2SO4
what is the reaction with PCl5 with alcohols?
white / misty fumes of HCl
how is bromoalkanes formed with alcohols?
potassium bromide (KBr) + 50% concentrated H2SO4
how is iodoalkanes formed with alcohols?
PI3 (produced in situ with red phosphorus & iodine)
why couldn’t tertiary alcohols be oxidised by potassium dichromate?
there’s not hydrogen atoms bonded to the carbon with the -OH group attached
what tests are used to distinguish aldehydes & ketones?
Fehling’s solution / Benedict’s solution
what is the reaction & observation with aldehydes and Fehling’s solution?
aldehydes are oxidised into carboxylic acids & Cu2+ ions are reduced into copper(I) oxide
blue Cu2+ ions change into brick-red precipitate of copper(I) oxide
what is used to test for a carboxylic acid?
addition of sodium carbonate; effervescence
why is ethanol and excess NH3 needed in nucleophilic substitution of halogenoalkanes to amines?
ethanol: solvent for organic compounds
excess NH3: neutralises acid produced (H+)