Topic 17 Flashcards
What is chirality?
The arrangement of the molecule (shape of molecule) affects the biological process
What is the difference between mirror and superimposable molecules?
****Mirror Molecules******
- Molecules of the same type
- Mirror images of each other
Super Imposable
- If the two mirror molecules are put on top of one another
- If they do NOT match then they are superimposable
What makes 2 molecules chiral to each other?
- The two molecules have to be **********Mirror molecules of each other********** and ******Super Imposable******
- Properly exclusive to asymmetrical molecules with different groups attached to a central carbon atom
What are chiral centres?
A carbon atom has four different groups bonded to it in such a manner that it has a non-superimposable mirror image.
What effect do different chiral centres have?
- Different arrangements of chiral centres have different effects on the body (can be used for medicines)
- Some of these mirror terms have to be separated and artificially created
What is plane-unpolarised light?
Unpolarised light
- Multiple directions of travel of the wave
- Multiple different directions of oscillations
What is plane-polarised light?
******Polarised Light******
- One direction of travel of the wave
- One direction of oscillation
- Occurs on one plane
How do you convert unpolarised light to polarised light?
- Synthetic material like a polaroid
- Has horizontal lines which can absorb all of the oscillations except those in a single plane
- Single plane assumed to be vertical
What is polarimetry?
The use of a polarimeter to measure the amount of optical activity
How does a polarimeter work?
- Monochromatic light source
- Passes through polarising filter
- Called a polariser
- Conversion of unpolarised → vertically plane-polarised light
- Polarised light passes through a sample tube containing sample
- Plane of polarisation so its no longer vertical through rotation
- Dextrorotatory = clockwise
- Laevorotatory = anti-clockwise
- Analyser is a second polarising filter
- Rotated to a position where the maximum light intensity can be seen
- Angle of rotation is measured
- Quoted positive value if rotation is clockwise
- Quoted negative value if rotation is anticlockwise
- Measured in alpha waves
What is a racemic mixture?
Enantiomers which are made in a 50/50 mix is known as a racemic mixture
What can enantiomers cause?
- Cause plane polarised light to rotate
- Either to the left or to the right
What effect does polarised light have on racemic mixture?
- Due to the nucleophile being being able to attack from above and below
- A 50/50 mic of enantiomers is made (racemic mixture)
- Meaning polarised light has no effect on the mixture
What is the SN1 mechanism?
- takes place in two steps
- R- represents alkyl groups
- central carbon has 4 different groups so has a chiral centre
- needs to have a chiral centre or it wont work
- if the intermediate (carbocation has lost a bond) is planar, the nucleophile can either attack from above or below
- when bonds are added/lost the shape changes (show this when drawing mechanisms )
- if the attack happens from above it will be a different shape compared to if the attack happens from below
- different arrangement depending on where the nucleophile has attacked from
- forms enantiomers which means they can rotate plane polarised light which is known as optical activity
- however, since this is a racemic mixture it has no effect on plane polarised light
What is the SN2 mechanism
- occurs in one step
- product will rotate plane polarised light
- tertiary carbocation is most stable so can only exist as a carbocation for a short period of time
- tertiary carbocation should undergo SN1 mechanism
- in reality the molecule going through SN1 would be primary or secondary haloalkane
- so for SN2 can only occur with a primary carbocation
What makes a carbonyl compound an aldehyde?
- If there is a hydrogen atom joined to a carbonyl group
- Has the suffix **-al** (Methanal)
- The general formula is RCHO
What makes a carbonyl compound an ketone?
- If there are only hydrocarbon groups joined to the carbonyl group
- Has the suffix **-one** (Propan**one**)
- The general formula is RCOR
What is the functional group of aldehydes?
What is the functional group of ketones?
What is the bonding in carboxyl groups?
- Polar double bond C=O
- Different electronegativities of carbon and oxygen******Unlike C=C which is non-polar********
- The electron density of the Pi bond is greater nearer the Oxygen atom
What are the physical properties of the Aldehydes and Ketones?
Physical Properties (Scents)
- Aldehyde Short carbon chain (Rancid)
- Aldehyde Long carbon chain (Nice Smells)
- Lower ketones smell like solvents (Propanone is used in nail varnish)
What are the boiling temperatures of aldehydes and ketones?
Boiling Temperatures
- Intermediate intermolecular force strength
- C=O polar bond means a permanent dipole-dipole interaction
- Lower BP than alcohols but higher than alkanes
What is the solubility of aldehydes and ketones in water?
Solubility in water
- Smaller chain aldehydes and ketones are ******soluble in water******
- Ability to form hydrogen bonds with water molecules
- Longer chain aldehydes and ketones ********are not soluble in water********
- The hydrocarbon part of the molecules outweighs the ability to form hydrogen bonds
What reactions occur involving aldehydes and ketones?
What are the reactions with LiAlH4
What is the Oxidation reaction for Acidified potassium dichromate?
What is the Oxidation reaction for Fehling’s Solution?
What is the Oxidation reaction for Benedict’s Solution?
What is the Oxidation reaction for Tollens Reagent
What are the reactions involving iodine in the presence of an alkali?
What is the reaction involving hydroxynitriles?
How can carboxylic acids be prepared through oxidation?
Oxidation
- Primary alcohol or Aldehyde
- Acidified potassium dichromate (oxidising agent)
- Heat under reflux
- Primary Alcohol → Aldehyde → Carboxylic acid
How can carboxylic acids be prepared through hydrolysis?
Hydrolysis
- Nitriles contain CN group
- It can be hydrolysed through heating under reflux
- With dilute hydrochloric acid
- Triple bond breaks
- Carbon acid remains part of organic product
- Nitrogen atom → ammonia or ammonium ion
What are the 4 main reactions to consider of a carboxylic acid?
What is the reduction reaction of carboxylic acids?
Reduction
- Carboxylic acids can be reduced into primary alcohols
- BUT NOT ********reduced into aldehydes********
- Aldehydes are ******easily reduced********
- So when reduced they will ******immediately form primary alcohols******
Butanoic acid → Butan-1-ol
What is the neutralisation reaction?
What is the halogenation reaction?
Halogenation
- Phosphorus(V) chloride in anhydrous conditions (both react in water)
- VIGOROUS REACTION no heating is required
- Where the OH group is replaced by a halogen atom (like chlorine)
- Forming a **COCl functional group****
- Acyl Chloride is formed (-oyl suffix), phosphorous oxychloride (requires distillation) and hydrogen chloride gas
What is the esterification reaction?
Esterification
- Carboxylic acid mixed with alcohol and a ******small amount******** of acid catalyst
- Reactions are still ******slow and reversible******
- Forming an ****ester link (**which can be used in industry and polymers**)****
- Which can be hydrolysed
methanoic acid + ethanol → ethyl methanoate + water
How are acyl chlorides formed?
- Through halogenation of a carboxylic acid
- Where the OH group is replaced Cl forming COCl group
- Resulting in the formation of a acyl chloride
How are acyl chloride reactions possible?
- Carbon atom in RCOCl is joined by O and Cl
- These are electronegative atoms
- Meaning that C is electro-deficient
- Meaning its readily attacked by nucleophiles
Why do we use acyl chlorides compared to carboxylic acids?
Acyl chlorides have a faster rate of reaction compared to carboxylic acids
What are the reaction with water
Water
- Vigorous reaction with ****cold water****
- Forms carboxylic acid + hydrogen chloride gas (mistry fumes)
What is the reaction with alcholos
Alcholos
- Forms an ester and hydrogen chloride gas (misty fumes)
What is the reaction with concentrated ammonia solution?
Concentrated Ammonia Solution
- Readily reacts with concentrated ammonia solution
- H of NH3 combines with Cl to form hydrogen chloride agas
- The other joins to dorm the cabonyl group
- Produceing an amide group
What is the further reactions of concentrated ammonia solution?
- Reactant is a base and the product is an acidic gas
- React together producing ammonium chloride
What is the combined overall reaction
What is the reaction with amines?
How do you name esters?
- Esters contain two words
- First comes from alkyl group joined to O
- Second comes from alkyl group joined to C
What are the physical properties of esters?
Physical Properties
- Low melting and boiling point
- Insoluble in water (no hydrogen bonding)
- Have different odors depending on chain length
What is the hydrolysis of esters in acidic solution?
Acidic solution
- Produces a carboxylic acid
- Warming an ester causes hydrolysis
- Slow reaction catalyst is required to speed up hydrolysis
- Doesn’t shift position of equilibrium meaning reaction wont go to completion
What is the hydrolysis of esters in an alkaline solution?
What is addition polymerisation?
Addition Polymerisation
- Monomers join together to form a polymer
- All atoms in the monomer end up in the structure of the polymer
What is condensation polymerisation?
Condensation Polymerisation
- Each time two monomers join a small product is made
- Can be water or other molecules like HCl
- Two different monomers join together
What is polyester?
- The reaction between alcohol and carboxylic acid
- Slightly larger ester molecule
What is required to form a polymer?
- Two monomers with two reactive groups at either end
- Alcohol (diol) has two reactive groups
- Dicarboxylic acid
Polyesters can also be formed from a single molecule with an alcohol and a carboxylic acid functional group present
