4.2 Flashcards
Describe the polarity of alcohols
- The OH group is polar and forms hydrogen bonds with water molecules and other alcohols
- So in small alcohols like ethanol the OH group forms hydrogen bonds with the water molecules which makes it soluble
Describe the boiling point of alcohols
The boiling point of an alcohol is high due to hydrogen bonding. Hydrogen bonding is a strong type of intermolecular forces found in all alcohols
How will the boiling point of alcohols change with increasing molecular size?
The boiling point will increase due to an increase in temporary dipoles (induced dipole forces)
Describe branching and its effect on boiling point for alcohols
Branching will lower boiling point as the induced dipole dipoles will coverless area. This will lower surface contact between the molecules, resulting in less energy being required to boil the alcohol
Compare boiling points between alcohols and alkenes
Boiling point will be much higher in alcohols dues to hydrogen bonding as they contain a polar OH group.
Compare solubility in water between alcohols and alkenes
Alcohols are soluble in water whereas alkenes aren’t. This is because the OH group is polar and forms hydrogen bonds with water molecules and other alcohols
Describe the volatility of alcohols
The OH group forms hydrogen bonds between alcohols which means that they have a relatively low volatility
Describe the trend in boiling point for straight chain alcohols
As chain length increases, boiling point increases. This is due to more energy being needed to overcome more temporary dipoles as well as hydrogen bondings
What are the 3 classifications of alcohols?
Primary
Secondary
Tertiary
What is meant by a primary alcohol?
A primary alcohol means the carbon the OH is on has one carbon attached (or 2 hydrogens attached)
What is meant by a secondary alcohol?
A secondary alcohol means the carbon the OH is on has two carbons attached to it (or has 1 hydrogen)
What is meant by a tertiary alcohol?
A tertiary alcohol means the carbon the OH is on has three carbons attached to it (or has no hydrogens)
Provide examples of secondary alcohols
Propan-2-ol
Butan-2-ol
Pentan-2-ol
Pentan-3-ol
Provide examples of tertiary alcohols
2-methylpropan-2-ol
2-methylbutan-2-ol
2-methylpentan-2-ol
3-methylpentan-3-ol
In the complete combustion of alcohols what 2 products are ALWAYS formed?
Water (H2O) and Carbon dioxide
In the complete combustion of alcohols what 2 products are ALWAYS formed?
Water (H2O) and Carbon dioxide
E.g. C2H5OH + 3O2 → 2CO2 + 3H2O
In the INCOMPLETE combustion of alcohols what 2 products are formed?
Either carbon monoxide (CO) or soot (C) and water (H2O)
What happens if you oxidise a primary alcohol under distillation?
It forms an aldehyde
Functional group - CHO
What happens if you oxidise an aldehyde?
It forms an carboxylic acid
Functional group -COOH
What happens if you oxidise if you a primary alcohol under reflux?
It forms an carboxylic acid
Functional group -COOH
What happens if you oxidise a secondary alcohol?
It forms a ketone
Functional group - CCOC
What happens if you oxidise a tertiary alcohol and why?
It won’t react as there are NO free protons to undergo the reaction mechanism
What is the oxidising agent when oxidising alcohols called?
Acidified Potassium dichromate
K2Cr2O7 / H2SO4
What colour is it? What colour does it change to when it has been reduced?
It is an ORANGE solution but turns GREEN when it has been reduced
NOTE: Bear in mind that oxidising agents get REDUCED
How can you represent acidified potassium dichromate?
[O]
What does acidified potassium dichromate get reduced to?
+6 to +3
In what situation will oxidation occur?
When the OH is attached to a carbon that has a hydrogen attached
Describe how primary alcohols oxidise to aldehydes
Provide a general equation
Primary alcohols oxidise to aldehydes and water if the oxidation is carried out under DISTILLATION
Primary alcohol + [O} + ( Under distillation) → Aldehyde + H2O
Describe how primary alcohols oxidise to carboxylic acids
Provide a general equation
Primary alcohols oxidise to carboxylic acid and water if the oxidation is carried out under REFLUX
Primary alcohol + [O} + ( Under REFLUX) → Carboxylic acid + H2O
Describe how secondary alcohols oxidise to ketone?
Provide a general equation
Secondary alcohols are EASILY oxidised to KETONES
Secondary alcohol + [O} → Ketone + H2O
NOTE: This process is also known as deydration
Describe a ketone
- Functional - CCOC
- The C=O group is NOT at the end of the chain
- The C doesn’t have a H on it
- It ends in in -one e.g. propanone
- If the C=O could be in more than one position, then a number is needed
Describe a aldehyde
- Functional group - CHO
- The C=O is always on the end of the chain
- They end in -al
- Aldehydes don’t have a number to show the position of the functional group because they are always at the end of the chain
Describe the elimination of H20 to form an alkene from an alcohol
Name - Dehydration
Reagent - Conc. sulfuric acid (H2SO4) or conc.phosphoric acid (H3P04)
Conditions = Reflux (180 degrees celsius)
Equation = Alcohol + (Reagent) → Alkene +H2O
Describe the process of changing an alkene to a halogenoalkane
Name - Electrophilic addition
Conditions - Room temperature
Equation = Alkane + Halogen → Dihaloalkane
Describe the process of forming an ester
Name - Esterification
Reagents - Carboxylic acid + Strong acid catalyst e.g. conc H2SO4
Equation - Carboxylic acid + Alcohol → Ester + H2O
Describe the process of making an alcohol from glucose
Name - Fermentation
Reagent - Glucose (From the hydrolysis of starch)
Conditions - Yeast, warm but not higher than 37 degrees celsisus
What is the functional group of a haloalkane?
C-X where X is a halogen (Br,Cl, I or F)
Explain the boiling point of haloalkanes
Increases as the compound gets bigger.
What is a nucleophile?
An electron pair donor
Describe a nucleophile
- Possess at least one LONE PAIR of electrons
- Don’t have to possess a negative charge e.g. NH3 or H2O
- They are attracted to the slightly positive carbon
Provide some examples of nucleophiles
OH- (Hydroxide ion)
CN- (Cyanide ion)
NH3 (Ammonia)
H20 (Water)
What is the process called that turns halogenoalkanes into alcohols?
Nucleophilic substitution
Outline nucleophilic substitution
Reagent - Aqueous sodium hydroxide [NaOH(aq)}
Conditions - Reflux (heat) in aqueous solution
Product = Alcohol + NaX (where X is a halogen)
Describe the nucleophilic substitution mechanism
- The nucleophile uses its lone pair to provide the electrons from a NEW BOND
- The halogen is displaced - (carbon can only make 4 bonds)
- The result is substitution following an attack by a nucleophile
Key Points of nucleophilic substitution
- The nucleophile has a lone pair of electrons
- The C-H bond is POLAR
- A curly arrow is drawn from the lone pair to the slightly positive carbon atom
- The polar C-H bond breaks
- The 2nd “curly arrow” shows the shared pair of electrons moving from the C-H bond onto the halogen
- A negatively charged halide ion is displaced
What is the most important reaction in nucleophilic substitution?
The breaking of the C-X bond
Where X is a halogen
Which haloalkane bond is the weakest out of : C - F C - Br C - Cl C - I What does this mean?
The C - I bond is the weakest so it will react the fastest. It is the weakest as it is the has the biggest atomic radius in group 7. This will lead to more shells being filled. As more shells are being filled, shielding (repulsion of outer electrons by inner electrons) will increase and the nuclear attraction between the outermost electron and nucleus will increase. This will mean that less energy will be needed to break the C - I bond, making the weakest and the most reactive
Which haloalkane bond is the strongest out of : C - F C - Br C - Cl C - I What does this mean?
The C - F bond is the strongest so it will react the slowest. It is the strongest as it is the has the smallest atomic radius in group 7. This means it only has a few shells (2 to be exact). As it only has 2 shells, it means that the outermost electron is very close to the nucleus so the bond between the two is very strong. As the bond is very strong, a ton of energy will be required to break the bond meaning that it will react very slow.
How can we determine the rate of hydrolysis?
By reacting haloalkanes with water in the presence of silver nitrate, AgNO3 and ethanol
When the halide ion is placed by the OH- ion, Ag X is formed.
The quicker the precipitate forms the faster the rate of hydrolysis
Where X is halogen
What colour is the Chlorine (Cl-) precipitate?
White PPT
What colour is the Bromine (Br-) precipitate?
Cream PPT
What colour is the Iodine (I-) precipitate?
Yellow PPT
When looking at the upper atmosphere what reactions must we know?
CFC’s
NO radical reaction
Outline the reaction of CFC’s undergoing free radical substitution
Initiation - CF2CL2 + (UV) → CF2Cl• + Cl•
Propagation - O3 + Cl• → O2 + •ClO
•ClO + O → Cl• +O2
Overall - O3 + 0 → 2O2
Use equations to show how a •NO radical can break down ozone (3 marks)
O3 + •NO → O2 + •NO2
•NO2 + O → •NO + O2
Overall - O3 + O2 → 2O2
CFC’S
- CFC’s have been blamed for damage to the environment by thinning the ozone layer
- Ozone absorbs a lot of harmful UV radiation
- However, it breaks down more easily in the presence of CFC’s
NOTE : The same is true for •NO
Why are CFC’s still in use?
- CFC’S are still very useful for certain things
- They are non - flammable and non - toxic
- They are used in refrigerators
- These must be disposed of carefully to reduce atmospheric CFC levels
What is the general formula for an alkane?
CnH2n+2
What is the general formula for an alkene?
CnH2n
What is the general formula for a haloalkane?
CnH2n+1X
What is the general formula for an alcohol?
CnH2n+1OH
What is Infrared Spectroscopy? (IR spec)
A technique used to identify unknown organic compounds
How to does IR spec work?
- It works by firing IR radiation at a compound.
- Different bonds absorb different amounts and frequencies of IR radiation.
- By seeing what frequencies are absorbed, the bonds in the compound can be identified.
- This is used to distinguish between alcohols, aldehydes/ketones and carboxylic acids
It is also used in breathalysers to detect alcohol levels.
What does IR radiation do to covalent bonds?
Causes them to VIBRATE more and absorb energy
What are the 3 bonds you must know for Infrared spec?
O-H
C-H
C=O
In what organic compound is the O-H bond found in?
Alcohols
Describe the absorbance of an alcohol
Strong and broad
Wavenumber (cm^1) of where you would find an alcohol
3230 - 3550
In what OTHER organic compound is the O-H bond in?
Carboxylic acid
Describe the absorbance of a carboxylic acid
Medium and very broad
Wavenumber (cm^1) of where you would find a carboxylic acid
2500-3500
In what organic compound is the C=O bond found in?
Aldehydes, Ketones and Esters (carbonyls)
Describe the absorbance of carbonyls
Strong and sharp
Describe the absorbance of a n aldehyde
1720-1740
Describe the absorbance of a ketone
1705-1725
Describe the absorbance of a ester
1735-1750
What does the x axis on an IR spectra represent?
Wavenumber
What does the y axis on an IR spectra represent?
Absorbance
NOTE: The stronger the absorbance, he larger the peak
What is meant by the fingerprint region?
- Organic molecules have a lot of C-C and C-H bonds within their structure
- All spectra will have peaks in the 1400 cm-1 to 800 cm-1 range
- This is referred to as the “fingerprint” region (unique for each chemical)
- This can be compared to a database to identify chemical
When identifying a functional group, do you include peaks in the “fingerprint” region?
NO YOU DON’T!!! NEVER DO THIS
Describe alcohols (talk about it’s shape and where you would find it etc)
Alcohols show a broad absorption between 3200 and 3600 cm^-1
This is due to the presence of the O-H bond
Describe carboxylic acids (talk about it’s shape and where you would find it etc)
- Carboxylic acids show a broad absorption between 3200 and 3600 cm^-1
- This is due to the presence of the O-H bond
- They also show a strong absorption around 1700 cm^-1
- This is due to the presence of the C=O bond
Describe carbonyl compounds (talk about it’s shape and where you would find it etc)
- Carbonyl compounds (ketones, aldehydes and esters) show a sharp, strong absorption between 1700 and 1760 cm^-1
- This is due to the presence of the C=O bond
Discuss IR and it’s use in breathalysers
Water in the breath can interfere with the O-H bond absorbance (at 3340cm^-1) but the sharp trough due to a C-H bond (at 2950cm^-1) can be used by a computer to calculate the percentage of ethanol present
Why do different compounds produce different IR spectra?
Different compounds contain different bonds, which absorb different wavelengths of IR
What are 5 stages needed for mass spectroscopy?
This works in several stages (VIADD) Vaporisation Ionisation Acceleration Deflection Detection
What is mass spec used for?
- Mass spectrometry can be used to work out the Mr of known compounds, or to identify unknown compounds in a sample.
- Mass spec is also used to monitor pollution levels, to test athletes for banned substances, and even to identify elements on mars
Identifying Unknown Compounds
- The peak with the highest m/z value is the total mass of the compound.
- The peaks with lower m/z values are fragments of the compound.
- These can be very useful in working out what the compound is.
Fragmentation
Common fragments CH3+ = 15 C2H5+ = 28 C3H7+ = 43 C6H5+ = 77 CO+ = 28
