CHEM UNIT 4

structural isomers

• Molecules with the same molecular formula where the atoms bond together in different arrangements

• resulting from branches in the carbon chain or different positions of the double bond

chain isomers

• formed due to different possible branchings in the carbon chain backbone

positional isomers

• Molecules that share the same carbon chain and functional group

• but have the functional group located on a different carbon atom

Geometric (cis–trans) isomers

• Isomers that occur when there is restricted rotation around a carbon–carbon double bond or within a ring

• leading to different spatial arrangements of attached groups

Cis isomer

• alkyl groups attached to the double-bonded carbon

• located on the same side of the double bond

Trans isomer

• the longest alkyl groups attached to the double-bonded carbon atoms are located on opposite sides of the double bond

Addition reaction

• A reaction where two reactant molecules combine to form a single product

• e.g conversion of a carbon–carbon double bond into a single bond as atoms are added across it

Hydrogenation reaction

• An addition reaction

• where an alkene reacts with hydrogen gas

• in the presence of a metal catalyst,

• such as nickel ($Ni$) to form a saturated alkane.

Bromine test

• A procedure used to identify the presence of a carbon–carbon double bond

• characterized by the rapid disappearance of the orange color of bromine

• when mixed with an alkene

Hydration reaction

• An addition reaction that involves water as a reactant

• such as the industrial production of ethanol from ethene and steam using a phosphoric acid catalyst at $300\,^\circ\text{C}$.

Addition polymerisation

• The process where small alkene molecules called monomers

• react with each other to form long-chain molecules called polymers

Monomer

• The individual small molecule unit, such as ethene

• that undergoes addition reactions to form a polymer.

Dispersion forces

• Weak forces of attraction between non-polar molecules like alkenes

• which increase in strength as the molecular size increases

• leading to higher boiling points.

alcohol

• compound with a hydroxyl group (-OH)

• can be classified as primary, secondary, tertiary

primary alcohol

• alcohol where the hydroxyl group is attached to a carbon atom

• that is only bonded to one other carbon

secondary alcohol

• alcohol where the hydroxyl group is attached to a carbon atom

• that is bonded to two other carbons

tertiary alcohol

• alcohol where the hydroxyl group is attached to a carbon atom

• that is bonded to three other carbons

how does the position of a hydroxyl group affect boiling point

• if —OH is central, the surrounding carbon chain block hydrogen bond interactions with another molecule, lowering BP

• terminal —OH groups are straight, have a greater surface area, and thus more dispersion forces, having a higher BP

why are small alcohols soluble in water

• due to their ability to form hydrogen bonds with water molecules

why are big alcohols insoluble in water

• as non-polar hydrocarbon chains get bigger, which increase the molecules dispersion forces

• these will overpower the hydrogen bonding ability of the hydroxyl group

• making them less soluble

use of alcohols

• fuels

• solvents

• beverages

aldehydes

• contain the carbonyl function group

• —CHO

• suffix: -al

how are aldehydes formed

• when primary alcohols are oxidised

what type of intermolecular forces do aldehydes have

• dipole-dipole due to C-O bond

• no hydrogen bonding

• dispersion forces

carboxylic acid

• contains the carboxyl group

• -COOH

how are carboxylic acids formed

• when aldehydes are further oxidised

• this can happen if the aldehyde is not removed

why do carboxylic acids have a high boiling point?

• due to strong hydrogen bonding

• and dimer formation

dimer hydrogen bonding

• where two molecules associate through multiple hydrogen bonds

ketone

• a carbonyl group bonded to two carbon atoms

• suffix: -one

how does a ketone form

through the oxidation of a secondary alcohol

alcohol oxidation

• is the process of converting an alcohol into a carbonyl compound

• involves the removal of hydrogen atoms

amines

• contain the amino functional group

• -NH2

• suffix: -amine

amide

• contains the carbonyl group attached to a nitrogen atom

• C-O, -NH₂

• suffix: -amide

what is the predominant intermolecular force in amines and amides

• hydrogen bonding

ester

• formed from an alcohol and a carboxylic acid

naming esters

• the -yl group from the alcohol first

• the acid's name ending in '-oate'.

thermoplastic polymers

• soften when warmed

• no cross links

elastomers

• occasional cross-links

• return to original shape

tetrafluoroethene

• used for non-stick cookware

• very strong dispersion forces

uses for PVC

• flooring

• pipes

• vinyl

• have dipole-dipole forces

LDPE

• many branches

• soft

• low MP/BP

• flexible

• poor packing

HDPE

• rigid

• no branches

• hard

• high MP/BP

polyesters

• formed from diols and dicarboxylic acids

• used for: fabrics, drink bottles

• have dipole-dipole forces

polyamides

• formed from diamines and dicarboxylic acids

• have hydrogen bonding

PET uses

• bottles

• packaging

• textiles

nylon uses

• clothing

• ropes

• parachutes

kevlar uses

• bulletproof vests

• tires

• aerospace components

uses for ldpe

• plastic bags

• wraps

• squeeze bottles

uses for hdpe

• playground equipment

• pipes

• milk jugs

Lipids

• Organic biological compounds

• include fats and oils

Animal Fats

are saturated

Plant Oils

are unsaturared

Triglycerides

• a triester made from 3 fatty acids and glycerol

• Large non-polar molecules

• insoluble in water as they cannot form hydrogen bonds.

• the main component of fats and oils

Fats

• Triglycerides that are solid

Oils

• Triglycerides that are liquid

Glycerol

A molecule also known as propan-1,2,3-triol which contains three hydroxyl ($-OH$) functional groups

Fatty Acids

Carboxylic acids with a carboxyl functional group ($-COOH$) attached to an unbranched hydrocarbon chain (tail) of $8$ or more carbons.

Condensation Reaction (Triglyceride Synthesis)

glycerol + 3 fatty acids → 3 ester links + 3H₂O

saturated Fatty Acids

single C-C bonds

monounsaturated Fatty Acids

one $C=C$ bond

polyunsaturated Fatty Acids

more than one $C=C$ double bond

uses of fats and oils

• in food directly

• fuel for cooking

• synthesis for other products (like soap, biodiesel)

saponification

• the conversion of basic solutions + fats/oils

• to form glycerol and a salt (soap)

hydrophobic tail

• a long, non-polar hydrocarbon chain

• repels water

hydrophilic end

• the head of the soap molecule

• is polar/ionic

• forms ion-dipole interactions with water

micelles

• a spherical, aggregate of a soap molecule in water

• these trap the oil in the centre

list the cleaning action of soap

• agitation to move micelles

• tails dissolve into oil

• heads stay in water and pull grease away

• grease is encapsulated in a micelle

• micelle prevents grease from reattaching to surface

• micelle dissolves in water

detergent

• a synthetic agent that breaks down grease and oils

• enhances the cleaning process by lowering surface tension of water

similarities of soaps and detergents

• both have a hydrophilic end and hydrophobic tail

• both form micelles

differences of soaps and detergents

• soaps contain a carboxylate group

• detergents contain a sulfonate group

biofuel

• a fuel derived from living matter (plant or animal)

biodiesel

• mixture of long chain fatty acid alkyl esters

transesterification

• reaction in where the alcohol-derived group of an ester is exchanged for another

biodiesel reaction

• triglyceride + 3 methanol → glycerol + 3 biodiesel

animal fuels (saturated) lead to…

• higher melting point

• poorer cold-flow behaviour

plant fuels (unsaturated) lead to…

• lower melting point

• better cold flow

lipase

• an biological enzyme

• breaks fats into fatty acids and glycerol

base catalysts

• has a short reaction time

• consist of NaOH or KOH

• low cost

• can promote soap formation

limitations of a lipase

• expensive

• function over a limited temp and pH range

layers in manufacturing biodiesel

• consists of a less polar, less dense biodiesel-rich layer

• and a more polar, denser glycerol-rich layer

how do i prevent waste from biodiesels?

• use waste cooking oil

• recover alcohol

• find use for glycerol

amino acid

• a compound which contains an amino group and a carboxyl group

• on the same alpha carbon

why are amino acids amphiprotic?

• —NH2 can accept H+

• —COOH can donate H+

zwitterions

• molecules that contain both positive and negative charges

• but are overall neutral

properties of zwitterions

• water solubility - polar groups interact with water

• high melting point - strong electrostatic attraction (ionic lattice)

peptide (amide) bond

• a covalent bond formed between the —COOH group

• and the —NH2 group

  
  

protein

• large, complex molecules made up of one or more chains of amino acids

polypeptides

• condensation polymer of amino acids

what is a primary structure?

• the number, type, and exact sequence of amino-acids

secondary structure

• the folding of the polypeptide

• results in α-helix and β-pleated sheets

alpha-helix

• a sequence of amino acids which forms a coil-shape

• are formed from the H-bonds of the amine and carbonyl group

beta-pleated sheets

• formed from hydrogen bonding between aligned regions

tertiary structure

• overall 3D shape

• contain both α and β structure

disulfide bridges

• covalent bonds between sulfur atoms

• forms between two cysteine amino acids

• stronger than h-bonds

how are proteins denatured by temperature?

• raising temps can weaken the dispersion forces between non-polar side chains

• this causes other stronger attractions to be increased

• tertiary structure will change

• leading to denaturation

how are proteins denatured by pH?

• changes the ionisation of acidic/basic side chains

• disrupts hydrogen and ionic bonds

• tertiary structure will change

• leading to denaturation

fermentation

• process which breaks down sugars

• to glucose

• to ethanol

conditions for the hydration of ethene

• high temperature (300 degrees)

• high pressure (7000 kPa)

• phosphoric acid

how is fermentation better?

• low energy use

• more environmentally friendly

• sustainable

• can be renewable

how is hydration of ethene better?

• high efficiency

• high purification

• is quicker