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[OBSELETE] Edexcel - A Level Chem > Topic 17 > Flashcards

Topic 17 Flashcards

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1
Q

What is chirality?

A

The arrangement of the molecule (shape of molecule) affects the biological process

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2
Q

What is the difference between mirror and superimposable molecules?

A

****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
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3
Q

What makes 2 molecules chiral to each other?

A
  • 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
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4
Q

What are chiral centres?

A

A carbon atom has four different groups bonded to it in such a manner that it has a non-superimposable mirror image.

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5
Q

What effect do different chiral centres have?

A
  • 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
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6
Q

What is plane-unpolarised light?

A

Unpolarised light

  • Multiple directions of travel of the wave
  • Multiple different directions of oscillations
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7
Q

What is plane-polarised light?

A

******Polarised Light******

  • One direction of travel of the wave
  • One direction of oscillation
  • Occurs on one plane
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8
Q

How do you convert unpolarised light to polarised light?

A
  • 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
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9
Q

What is polarimetry?

A

The use of a polarimeter to measure the amount of optical activity

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10
Q

How does a polarimeter work?

A
  • 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
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11
Q

What is a racemic mixture?

A

Enantiomers which are made in a 50/50 mix is known as a racemic mixture

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12
Q

What can enantiomers cause?

A
  • Cause plane polarised light to rotate
  • Either to the left or to the right
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13
Q

What effect does polarised light have on racemic mixture?

A
  • 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
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14
Q

What is the SN1 mechanism?

A
  • 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
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15
Q

What is the SN2 mechanism

A
  • 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
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16
Q

What makes a carbonyl compound an aldehyde?

A
  • If there is a hydrogen atom joined to a carbonyl group
  • Has the suffix **-al** (Methanal)
  • The general formula is RCHO
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17
Q

What makes a carbonyl compound an ketone?

A
  • If there are only hydrocarbon groups joined to the carbonyl group
  • Has the suffix **-one** (Propan**one**)
  • The general formula is RCOR
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18
Q

What is the functional group of aldehydes?

A
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19
Q

What is the functional group of ketones?

A
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20
Q

What is the bonding in carboxyl groups?

A
  • 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
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21
Q

What are the physical properties of the Aldehydes and Ketones?

A

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)
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22
Q

What are the boiling temperatures of aldehydes and ketones?

A

Boiling Temperatures

  • Intermediate intermolecular force strength
  • C=O polar bond means a permanent dipole-dipole interaction
  • Lower BP than alcohols but higher than alkanes
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23
Q

What is the solubility of aldehydes and ketones in water?

A

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
24
Q

What reactions occur involving aldehydes and ketones?

A
25
Q

What are the reactions with LiAlH4

A
26
Q

What is the Oxidation reaction for Acidified potassium dichromate?

A
27
Q

What is the Oxidation reaction for Fehling’s Solution?

A
28
Q

What is the Oxidation reaction for Benedict’s Solution?

A
29
Q

What is the Oxidation reaction for Tollens Reagent

A
30
Q

What are the reactions involving iodine in the presence of an alkali?

A
31
Q

What is the reaction involving hydroxynitriles?

A
32
Q

How can carboxylic acids be prepared through oxidation?

A

Oxidation

  • Primary alcohol or Aldehyde
  • Acidified potassium dichromate (oxidising agent)
  • Heat under reflux
  • Primary Alcohol → Aldehyde → Carboxylic acid
33
Q

How can carboxylic acids be prepared through hydrolysis?

A

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
34
Q

What are the 4 main reactions to consider of a carboxylic acid?

A
35
Q

What is the reduction reaction of carboxylic acids?

A

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

36
Q

What is the neutralisation reaction?

A
37
Q

What is the halogenation reaction?

A

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
38
Q

What is the esterification reaction?

A

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

39
Q

How are acyl chlorides formed?

A
  • Through halogenation of a carboxylic acid
  • Where the OH group is replaced Cl forming COCl group
  • Resulting in the formation of a acyl chloride
40
Q

How are acyl chloride reactions possible?

A
  • 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
41
Q

Why do we use acyl chlorides compared to carboxylic acids?

A

Acyl chlorides have a faster rate of reaction compared to carboxylic acids

42
Q

What are the reaction with water

A

Water

  • Vigorous reaction with ****cold water****
  • Forms carboxylic acid + hydrogen chloride gas (mistry fumes)
43
Q

What is the reaction with alcholos

A

Alcholos

  • Forms an ester and hydrogen chloride gas (misty fumes)
44
Q

What is the reaction with concentrated ammonia solution?

A

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
45
Q

What is the further reactions of concentrated ammonia solution?

A
  • Reactant is a base and the product is an acidic gas
  • React together producing ammonium chloride
46
Q

What is the combined overall reaction

A
47
Q

What is the reaction with amines?

A
48
Q

How do you name esters?

A
  • Esters contain two words
  • First comes from alkyl group joined to O
  • Second comes from alkyl group joined to C
49
Q

What are the physical properties of esters?

A

Physical Properties

  • Low melting and boiling point
  • Insoluble in water (no hydrogen bonding)
  • Have different odors depending on chain length
50
Q

What is the hydrolysis of esters in acidic solution?

A

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
51
Q

What is the hydrolysis of esters in an alkaline solution?

A
52
Q

What is addition polymerisation?

A

Addition Polymerisation

  • Monomers join together to form a polymer
  • All atoms in the monomer end up in the structure of the polymer
53
Q

What is condensation polymerisation?

A

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
54
Q

What is polyester?

A
  • The reaction between alcohol and carboxylic acid
  • Slightly larger ester molecule
55
Q

What is required to form a polymer?

A
  • 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

[OBSELETE] Edexcel - A Level Chem (27 decks)

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