4.2 Alcohols, Haloalkanes And Analysis Flashcards
Why is the boiling point of alcohols higher than that of their corresponding alkane?
-as their are hydrogen bonds between the alcohol molecules
-this is the strongest type of intermolecular bond
-more energy is needed to overcome this intermolecular force than the London intermolecular forces in alkanes
Why are alcohols less volatile than their corresponding alkane?
-due to the hydrogen bonding in alcohols that is not present in alkanes
Describe water solubility in an alcohol
-water molecules are polar and so is the alcohol functional group
-meaning some alcohols (methanol,ethanol and propanol) are soluble in water
-their molecules form hydrogen bonds with the molecules, sometimes described as miscibility
What happens to the solubility of an alcohol as their alkyl chain length increases?
-the solubility of an alcohol decreases
-because the aliphatic chain cannot form hydrogen bonds and this becomes the larger part of the molecule
What happens if you oxidise a primary alcohol with K2Cr2O7 with gentle heating?
-the alcohol group loses its hydrogen and is partially oxidised to an aldehyde-the alcohol must be distilled immediately to prevent any further reaction
-colour change from orange to green
What happens if a primary alcohol is heated under reflux with excess K2Cr2O7?
-full oxidation occurs to form a carboxylic acid
-colour change from orange to green
How do you form a ketone ?
-oxidise a secondary alcohol by heating it under reflux with K2CrO7 (acidified potassium dichromate (VI)
-colour change from orange to green
Are tertiary alcohols oxidised by acidified potassium dichromate (VI)?
-no tertiary alcohols are very resistant to oxidation and are not oxidised by common oxidising agents
What is the esterification of alcohols
-making an ester by reacting an alcohol with a carboxylic acid
-conditions:
.sulfuric acid as a catalyst
.80 degrees Celsius
How are alkenes formed from alcohols?
-this is an elimination reaction(H2O is eliminated)
-conditions:
.in the presence of an acid catalyst (H2SO4 -sulfuric acid)
.170 degrees Celsius
What makes haloalkanes?
-a substitution reaction with halide ions in the presence of an acid (such as concentrated sulfuric acid) mixture is warmed
Define a nucleophile?
An electron pair donor
What is the test for an unsaturated hydrocarbon (alkene)?
-add a few drops of bromine water to the sample and shake
-bromine water decoloursises the sample
What is the test for the haloalkanes?
-add silver nitrate, ethanol and water
-white precipitate indicates chloro-
-cream precipitate indicates bromo-
-yellow precipitate indicates iodo-
What happens if you add acidified potassium dichromate to carbonyls?
-ketones- no change
-aldehyde - orange turns green
What happens if you add fehling’s solution to carbonyls?
-ketones-no change
-aldehydes- silver mirror
What happens if you add Tohlen’s reagent to carbonyls?
-ketones-no silver mirror
-aldehydes -no silver mirror
What is the pH of a carboxylic acid?
-pH of a weak acid
What observation can you see if you add a reactive metal like Mg to a carboxylic acid?
-effervescence (hydrogen)
What observation can you see if you add a metal carbonate to a carboxylic acid?
-effervescence (carbon dioxide)
How can you test for the OH functional group of an alcohol?
-warm with an equal volume of carboxylic acid and a few drops of H2SO4
OBSERVATION- the sweet smell of an ester after a short time
What is the link between infrared radiation and global warming?
-as we release more greenhouse gases into the atmosphere more infrared radiation can be absorbed this leads to global warming
-this has influenced governments to introduce policies that encourage the use of technologies and energy resources that do not release greenhouse gases into the environment
What does infrared radiation do to covalent bonds?
-it causes covalent bonds to vibrate more and absorb energy
What is infared spectroscopy used in (in everyday life?)
-to monitor gases causing air pollution (e.g. CO and NO from car emissions)
-in modern breathalysers to measure ethanol in breath
Infared radiation causes covalent bonds to _________ ______ and ___________ _________
-vibrate more
-absorb energy
What does the molecular ion produce on a mass spectrometer?
-the molecular ion produces the peak with the highest mass/change value in the mass spectrum (peak furthest to the right)
What are five m/z values on a mass spectrometer for common fragment ions?
What is a primary alcohol?
The carbon that is bonded to the oxygen is also bonded to one other carbon
What is a secondary alcohol?
The carbon that is bonded to the oxygen is also bonded to two other carbon atoms
What is a tertiary alcohol?
The carbon that is bonded to the oxygen is also bonded to three other carbons
Draw the mechanism for hydrolysis of 1-chloropropane with an aqueous alkali
How does the halogen in the primary haloalkane affect the rate of hydrolysis? Why?
Rate of hydrolysis increases down group 7 because the bond enthalpy of the carbon-halogen bond decreases down the group meaning less energy is needed to break this bond. This means hydrolysis of iodoalkanes will form a precipitate the fastest.
How do you form an alkene from an alcohol?
-elimination of water from alcohols in the presence of an acid catalyst (sulfuric acid or phosphoric acid)
-and heat
-forms alkene
How do you form an haloalkane from an alcohol?
-substitution with halide ions in the presence of acid (NaBr / H2SO4)
-forms haloalkane
State two limitations of using radical substitution in organic synthesis
(2marks)
-further substitution/ mixture of products formed/more than one termination step
-substitution at different positions along the chain
