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CHEMISTRY U3/4 > REACTION PATHWAYS > Flashcards

REACTION PATHWAYS Flashcards

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1
Q

alkane subsitution reactions

A
  • occurs when an atom or functional group in a molecule is substituted by another atom or group
    • alkanes can undergo substitution reactions with halogens such as Cl and Br to produce haloalkanes
    • won’t occur at room temp or in the dark and must be initiated with UV light
  • if enough halogen is present - successive hydrogens can be replaced producing a range of haloalkane products
  • these products will have different boiling points and can be separate by fractional distillation
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2
Q

electronegativity

A
  • ability of an atom to attract electrons towards itself when forming a chemical bond
    • electronegativity difference= higher electronegativity value - lower electronegativity value
    • increases across the period and decreases down the group
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3
Q

haloalkane substitution reactions

A
  • substitution reaction
  • the halogen is swapped for a hydroxyl group
  • the reactions of haloalkanes with hydroxide ions can be represented as:
    • OH- + RCl → ROH where R is an alkyl group
  • can also react with ammonia in substation reactions to form an amine
  • no catalyst is req
  • AMMONIA ONLY REACTS WITH HALOALKANES not alkanes
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4
Q

reaction of alkenes

A
  • combusition in air
  • addition reactions
    • reacting with H2 - hydrogenation
    • reacting with halogens
    • reacting with hydrogen halides (HCl, HF)
    • reacting with water - hydration reaction
    • addition polymerisation
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5
Q

addition reactions - alkenes

A
  • involve the addition of a small molecule to the double bond of the alkene
  • 2 reactant molecules combine to form 1 product
  • carbon-carbon double bond becomes a single bond
  • unsaturated alkene becomes saturated
  • no inorganic product form
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6
Q

addition reaction with hydrogen

A

alkenes react with H2 gas in the presence of a catalyst (eg. nickel)
- forms alkanes

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7
Q

reactions of alkenes with halogens

A
  • can proceed at room temp w/o catalyst
  • each halogen atom attaches to a carbon atom that forms a double bond
  • the product is known as a di-substituted haloalkane
  • used to test for double bonds
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8
Q

reaction of alkenes with hydrogen halides

A
  • 2 isomers can form
    • position of hydrogen and the halogen atom creates diff isomers
  • forms a haloalkane
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9
Q

reactions of alkenes with water

A
  • only react w water under specific conditions
    • 300 degrees Celsius and with a phosphoric acid catalyst (H3PO4)
    • SPEEDS UP RATE OF REACTION
  • gaseous reactant passed over solid bed of the catalyst easy to separate product - heterogenous reaction system
  • produces alcohol
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10
Q

addition polymerisation of alkenes

A
  • undergo addition reactions with themselves
  • starting compound is a monomer and the product is a polymer
  • polymers are represented with square brackets around repeating unit and a subscript n which represents no. of repeating units
  • average length of polymer is about 20000 carbons
  • monomer ethene → polyethene
  • monomer propene →polypropene
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11
Q

reactions of alcohols

A
  • undergo two reactions
    • combustion
    • oxidation
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12
Q

combustion of alcohols

A
  • used as a fuel
  • combustion of alcohol is a type of redox reaction
    • OXIDATION: gain of oxygen and loss of hydrogen
    • REDUCTION: loss of oxygen and gain of hydrogen
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13
Q

oxidation of alcohols

A

alcohols can be oxidised by strong inorganic oxidising agents such as acidic solutions of potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4)

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14
Q

oxidation of primary alcohols

A
  • can be oxidised to a carboxylic acid in 2 steps
  • first oxidised to an aldehyde (intermediate) which is then further oxidised to a carboxylic acid
  • to produce an aldehyde
    • milder conditions are used
    • shorter reaction time
    • lower temperatures
  • to produce carboxylic acid
    • longer reaction times and higher temperatures
  • general equations for organic chemistry are not balanced and the formula of the inorganic reactants are written above the arrow
  • only organic products are shown
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15
Q

oxidation of secondary alcohols

A

can be oxidised by strong oxidising agents (H+/Cr2O7^2- and H+/MnO4^-) to form ketones

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16
Q

oxidation of tertiary alcohols

A
  • cannot be oxidised
  • carbon attached to hydroxyl group does not have C-H bond to break so oxidation cannot occur at that carbon
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17
Q

reactions of carboxylic acids

A
  • ionisation in water
  • condensation reactions which incl
    • esterification (condensation)
    • formation of amides
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18
Q

ionisation in water - carboxylic acids

A
  • are weak acids and don’t ionise completely
  • reaction of carboxylic acid with water is a reversible process
  • equilibrium constant is small - so equilibrium position favours the reactants
  • only ionises partially in water
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19
Q

esterification

A
  • reaction between carboxylic acid and alcohol produces an ester
  • also known as a condensation reaction → combination of 2 creation results in the elimination of a small molecule in this case - H2O molecule
  • requires a catalyst (concentrated H2SO4) and heat to speed up the reaction (delta sign)
  • also a reversible reaction
    • a hydrolytic reaction (hydrolysis)
    • as esterification and hydrolytic reaction req diff reaction conditions, we don’t use reversible arrows and write them as separate reactions
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20
Q

carboxylic acids and ammonia

A
  • forms amides
  • hydroxyl group swapped with amine group
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21
Q

reaction of esters

A

undergoes hydrolysis and transesterification

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22
Q

hydrolysis of esters

A
  • produces alcohol and carboxylic acids
  • hydro - water, lysis - break apart
  • reverse process of condensation reaction between alcohols and carbocyclic acids
  • requires a catalyst - dilute acid or alkali
23
Q

transesterification

A
  • triglyceride and small alcohol molecule (methanol) in the presence of catalyst (KOH)
    • alkyl group on ester and on the alcohol molecule swap places
  • produces fatty acid esters - biodiesel
24
Q

reaction pathways

A

sequence of reactions to produce a specific product

25
Q

green pathway

A
  • fewer reactants are needed
  • higher proprotion of atoms in the reactants are present in the final product (high atom economy)
  • less waste
26
Q

actual yield

A

amount of desired product formed in the reaction

27
Q

theoretic yield

A
  • mass of product that can be formed if the limiting reactant reacts according to the stoichiometric ratio in the balanced chemical equation
  • assumes 100% conversion of reactants
28
Q

percentage yield

A
  • the higher the percentage yield the greater the degree of conversion from reactants to products
  • more efficient
  • % yield = actual yield/theoretical yield x 100
29
Q

atom economy

A
  • the measure of the percentage of atoms in the reactants that end up in the desired products
  • aim to have high atom economy → few waste products
  • atom economy = molar mass of desired product/molar mass of all reactants x 100
30
Q

green chemistry

A
  • using renewable feedstock - raw materials
    • using biodegradable materials that don’t persist as wastes in the environment
      • biopolymers like celluloid/cellophane
      • biosolvents
  • using catalysts
    - not consumed in reaction → can be used multiple times and continuously
  • increases rate of reaction - so very high temperatures aren’t required
    • reduced heating cost and saves energy resources
  • reduces need for chemicals and minimises waste production
  • designing safer chemicals and products that are effective
    -banning dangerous chemicals so fewer compounds enter the environment
31
Q

proteins

A
  • organic biopolymers such as enzymes - made from building blocks - amino acids
  • formed using condensation polymerisation reactions
32
Q

amino acids

A
  • amino group (-NH2)
  • carboxyl group (-COOH)
  • a hydrogen attached to the central carbon atom (alpha - carbon)
  • R group - which varies between amino acids
    • can be non-polar
    • charged - +/-
    • polar but uncharged
33
Q

zwitterions

A
  • amino acids contain polar amine and carboxyl groups - soluble in water
    • NH2 can act as a base - accept a proton to become a -NH3+ group
    • COOH can act as an acid - donate a proton to become as -COO- group
    • becomes a zwitterion - dipolar ions with no overall charge
      • due to its dual acidic and basic nature - diff chemical forms of amino acids can be in equilibrium in a solution
  • predominant form depends on pH of solution
  • low pH
    • becomes a cation
    • presence of excess H+ favours cation form (NH3+)
  • high pH
    • becomes an anion
    • presence of excess OH- ions favours an anion form (COO-)
34
Q

forming proteins

A
  • 2 types of condensation polymerisation reaction - depending on the reactive functional group on either end of amino acid
  • occurs between -COOH group of an amino acid and -NH2 group of another amino acid
  • an AMIDE group (peptide link) joins the two amino acids
  • water is released during reaction
  • 2 amino acids - dipeptide
  • 3 amino acids - tripeptide
  • many amino acids - polypeptide
  • greater than 50 amino acids - protein
  • for each pair of amino acids, there are 2 possible product molecules depending on which ends of each molecules react tgt
  • stepwise process - new amino acids are added to existing polypeptide chain
  • naming - amino acids separated by dashes
35
Q

homopolymer vs heteropolymer

A
  • homopolymer
    • two different functional groups on one monomer (most biological polymers are homopolymers)
    • requires only 1 type of monomer to form a homopolymer
  • heteropolymer/copolymer
    • each monomer has the same functional group on either end (most synthetic polymers)
    • requires 2 diff types of monomers to form heteropolymer
36
Q

insulin

A
  • smallest protein in the human body and regulates the metabolism (breakdown) of carbohydrates, fats, proteins
  • 2 linked chains - total of 51 amino acid residues
  • A - 21 amino acids, B- 30 amino acids
  • chains are linked by covalent bonds between sulfur atoms from R group of cystine residuals
    • have S-H (thiol) group and when they react a disulfide bond (S-S) forms
    • start of longer chain has free amino group on Phe - N terminal amino acid of chain
    • end of chain is Thr - has free carbonyl group - C terminal amino acid
37
Q

carbohydrates

A
  • nutrients made up of 3 types of atoms - carbon, hydrogen and oxygen
  • general formula Cx(H2O)y
  • monosaccharides, disaccharides, polysaccharides
38
Q

monosaccharides

A
  • smallest carbohydrates - white sweet tasting solids
  • most common: glucose, gallactose, fructose
    • are structural isomers with the same molecular formula C6H12O6
    • position of hydroxyl group in glucose and galctose - leads to diff in their functions
  • have several polar hydroxyl groups
    • can form hydrogen bonds in water - highly soluble
39
Q

disaccharides

A
  • when 2 monosaccharides molecules react
  • condensation reaction between the 2 hydroxyl functional groups of neighbouring molecules and a water molecule is formed as a by product
  • monosaccharides are joined by an ether link (gylcosidic link in carbohydrates)
  • examples
    • maltose: 2 glucose molecule reacts
    • sucrose: fructose and glucose reacts
    • lactose: galactose and glucose
40
Q

polysaccharides

A
  • generally insoluble and no taste
  • eg. starch, cellulose and glycogen - all polymers of glucose
  • in solution glucose can exist as 3 isomers
  • in polymers of glucose there are 2 forms of glucose (alpha-glucose and beta-glucose)
41
Q

polysaccharide - starch

A
  • plants produce polymerised alpha glucose molecules to form starch
  • condensation reaction - glycosidic links
  • 2 types - linear and branched
  • amylose - linear form
    • long molecules that coil in spiral like helices and pack tightly together
    • many hydroxyl groups are inside the helices - away from contact with water
    • largely insoluble in water
  • amylopectin - branched form
    • forms if some glucose molecules undergo condensation reactions between hydroxyl groups at diff positions around the glucose ring
    • results in occasional branches in structure
    • branches are around 20-24 glucose units
    • branches restrict polymer from coiling - leaves many hydroxyl groups exposed to water
    • soluble in water
42
Q

polysaccharide - cellulose

A
  • structural material in plants
  • very large, straight chain polymer of beta glucose
  • in starch -CH2OH group remains on same side of polymer
  • in cellulose - CH2OH group alternates between diff side of poymer 0 allows for good alignment of hydroxyl groups between neighbouring molecules
  • allows hydrogen bonding -strong material
43
Q

polysaccharide - glycogen

A
  • formed when alpha glucose polymerises
  • similar to amylopectin - but is HIGHLY BRANCHED
  • for energy storage in animals
  • formed from excess glucose and stored in liver or muscle tissues and can be broken down into glucose for energy
44
Q

lipids

A
  • fats are solid at room temp and oils are liquid at room temp
  • fats and oils are produced by plants
  • fats can be produced by animals - store chemical energy
45
Q

triglycerides

A
  • fats and oils are made up of large non-polar molecules called trigylcerides
  • cannot form hydrogen bonds w water
  • triglyceride is made up of a glycerol backbone and 3 fatty acid tails
    • is fatty because of the long non-polar hydrocarbon chain
    • tails make up most of molecule and have even no. of carbon atoms
  • are formed by condensation reaction between 1 glycerol and 3 fatty acids
  • results in the formation of 3 ester links and release 3 water molecles per triglyceride molecule
  • fatty acid chain on a triglyceride molecule can differ - in length and some may have double carbon bonds

ARE NOT POLYMERS

46
Q

saturated vs unsaturated fatty acids

A

saturated fatty acids

  • contain only single C-C bonds
  • general formula: CnH2n+1COOH

monounsaturated fatty acids

  • contain only one double carbon bond
  • general formula CnH2n-1COOH

polyunsaturated fatty acids

  • contains more than one carbon carbon double bond
  • general formula CnH2n-3COOH
47
Q

hydrolysis of carbohydrates

A

starch and glycogen

  • maltase breaks down maltose into glucose
  • glucose is highly soluble - dissolves in blood and is transported to places where energy is required

cellulose

  • humans don’t have cellulase enzyme to hydrolyse cellulose
  • passes through digestive system unchanged
48
Q

hydrolysis vs condensation reactions

A

hydrolysis

  • splitting of larger molecules by reacting with H2O

condensation

  • joinign 2 smaller molecules to form larger molecule
  • eliminate H2O
49
Q

hydrolysis of proteins

A
  • broken down into individual amino acids
  • HCl and muscular contractions unravel 3d structure of protein
  • proteases (pepsin - main one) break down polypeptide chain - becomes dipeptides then single amino acids in small intestine
50
Q

hydrolysis of lipids - triglycerides

A
  • catalysed by lipase enzyme
  • insoluble in water - remain intact until small intestine
  • bile emulsifies fat → fat globules to smaller fat droplets
    • lipase is water soluble - can only interact with the surface of non-polar fat globules
    • emulsifying increases surface area
    • lipase can access more triglyceride molecules
  • lipase comes from pancreas - hydrolyses the ester bonds
51
Q

fats vs oils

A
  • Saturated fatty acids form straight chains.
  • The corresponding triglyceride molecules can pack closely to each other.
  • Tend to be fats (higher m.pts.)
  • The double C=C bond puts a kink in the chain of mono unsaturated and poly-unsaturated fatty acids
  • The corresponding triglycerides cannot pack closely to each other
  • Tend to be oils (lower m.pts.)
52
Q

2 WAYS TO PRODUCE BIODIESEL

A
  • fatty acid + methanol (with sulfuric acid) -> biodiesel
  • triglyceride + methanol (with KOH) -> glycerol and 3 biodiesel molecules
53
Q

why is theoretical yield not achieved

A
  • not achieved because:
    • reactions reaching equilibirum - doesn’t continue on to completion
    • reaction rate is slow - reaction may not proceed to completion in the time available
    • competing reactions → unwanted side reactions that don’t produce desired product
    • decomposition of product

CHEMISTRY U3/4 (11 decks)

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