REACTION PATHWAYS Flashcards
(53 cards)
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
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
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
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
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
6
Q
addition reaction with hydrogen
A
alkenes react with H2 gas in the presence of a catalyst (eg. nickel)
- forms alkanes
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
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
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
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
11
Q
reactions of alcohols
A
- undergo two reactions
- combustion
- oxidation
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
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)
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
15
Q
oxidation of secondary alcohols
A
can be oxidised by strong oxidising agents (H+/Cr2O7^2- and H+/MnO4^-) to form ketones
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
17
Q
reactions of carboxylic acids
A
- ionisation in water
- condensation reactions which incl
- esterification (condensation)
- formation of amides
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
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
20
Q
carboxylic acids and ammonia
A
- forms amides
- hydroxyl group swapped with amine group
21
Q
reaction of esters
A
undergoes hydrolysis and transesterification
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
green pathway
- fewer reactants are needed
- higher proprotion of atoms in the reactants are present in the final product (high atom economy)
- less waste
26
actual yield
amount of desired product formed in the reaction
27
theoretic yield
- 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
percentage yield
- 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
atom economy
- 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
green chemistry
- 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
proteins
- organic biopolymers such as enzymes - made from building blocks - amino acids
- formed using condensation polymerisation reactions
32
amino acids
- 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
zwitterions
- 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
forming proteins
- 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
homopolymer vs heteropolymer
- **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
insulin
- 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
carbohydrates
- nutrients made up of 3 types of atoms - carbon, hydrogen and oxygen
- general formula Cx(H2O)y
- monosaccharides, disaccharides, polysaccharides
38
monosaccharides
- 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
disaccharides
- 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
polysaccharides
- 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
polysaccharide - starch
- 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
polysaccharide - cellulose
- 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
polysaccharide - glycogen
- 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
lipids
- 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
triglycerides
- 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
## Footnote
ARE NOT POLYMERS
46
saturated vs unsaturated fatty acids
**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
hydrolysis of carbohydrates
**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
hydrolysis vs condensation reactions
**hydrolysis**
- splitting of larger molecules by reacting with H2O
**condensation**
- joinign 2 smaller molecules to form larger molecule
- eliminate H2O
49
hydrolysis of proteins
- 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
hydrolysis of lipids - triglycerides
- 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
fats vs oils
* 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
2 WAYS TO PRODUCE BIODIESEL
* fatty acid + methanol (with sulfuric acid) -> biodiesel
* triglyceride + methanol (with KOH) -> glycerol and 3 biodiesel molecules
53
why is theoretical yield not achieved
- 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
