VCE Chemistry Unit 4

Hydrocarbons

molecule consisting of C and H only

Isomer

molecules with the same molecular formula, but have a different arrangement of atoms

Alkanes

Contain singly C-C bonds, fully saturated

Alkenes

Contain at least one C=C bond, are unsaturated

Degree of unsaturation

number of C=C bonds in a molecule
Formula= no. H atoms missing/2

Arenes (benzenes)

Most common is C₆H₆ aka benzene

Contain a ring of delocalised e^-

Haloalkane

Organic compound with a halogen atom

Halogens named in alphabetical order

Alcohol

Have a hydroxyl group attached

Primary: Group attached to C attached to only one other C

Secondary: Group attached to C attached to 2 other Cs

Tertiary: Group attached to C attached to 3 other Cs

Amines

-NH₂

Name: amino

Suffix: -amine

Aldehydes

C=O

Name: carbonyl

Suffix: -al

Ketones

C=O (not primary)

-CO-

Carboxylic acids

-COOH

Name: carboxyl

Suffix: -oic acid

Primary amides

-CONH₂

Naming not required for study design

Esters

-COO-

Name: ester

Suffix: -oate

Formed through condensation of primary alcohol and carboxylic acid

Bonding for Carboxylic acids

Can form 2 hydrogen bonds per molecule, resulting in the formation of a dimer. Much stronger bond than many other organic compounds with hydrogen bonds.

Viscosity

Measure of a liquid’s resistance to flow.

More viscous, less flow

Substitution reaction

An atom or group of atoms is replaced by another atom or group of atoms.

Must be in the presence of UV light

Addition reaction

An unsaturated bond is saturated through the addition of an atom or group of atoms.

e.g. HBr, Cl₂ all react to saturate double bonds

Addition of halogens/hydrogen halides don’t require any catalysts

Addition of Hydrogen

Hydrogenation reaction, between an alkene and hydrogen

Requires a catalyst to react

e.g. Nickel, Platinum

Addition of Water

Hydration reaction (involves water/steam)

Requires presence of solid H₃PO₄ catalyst (phosphoric acid) and heat

Substitution of haloalkanes

-OH, NH₃

Require no catalyst as bond is reactive enough

H₂O

Produces alcohol, requires a catalyst (e.g. Iron oxide) and heat

Oxidation reaction

Alcohols can be oxidised depending on their structure

Distillation:

Primary, secondary alcohols → aldehyde, ketone

Reflux:

Primary → Carboxylic acid

*Tertiary alcohols can not be oxides

Oxidising agents: MnO₄^- or Cr₂O₇^- (with H⁺)

Reactions of carboxylic acids

Act as weak acids, partially ionise in water

React fully with bases and carbonates/hydrogen carbonates

Esterification reaction

also condensation reaction, as water is produced

Carboxylic acid + alcohol with conc. H₂SO₄ and heat

Hydrolysis of an ester

Add water with acid catalyst

Transesterification reaction

Triglyceride converted to biodiesel

Reacts an alcohol + ester

Presence of catalyst e.g. KOH or NaOH

From 3 ester molecules + 1 glycerol molecule

Yield for multistage process

(decimal yield of all x each other) x 100

Proteins

Growth, repair of tissues

Meat, eggs, lentils

Carbohydrates

Dietary fibre

Starchy foods

Fats + oils (triglycerides)

Carrier for fatty acids

Butter, oils, fats

Amino acids

Carboxyl group

Amino group

R’ group → on second carbon

Formation of proteins

Condensation reaction, forms peptide/amide bond

[-OH from carboxyl, H for amino]→ combine

Carbohydrates

monosaccharide

disaccharide

polysaccharide

Made from C, H and O

Monosaccharides

Glucose (α and β)

Fructose, galactose

Disaccharides

Form glycosidic link/ether bond between monosaccharides

(C-O-C)

Condensation reaction

Polysaccharides

Very large, no taste, generally insoluble in water

e.g. starch, cellulose, glycogen

Starch

α-D-glucose

creates:

amylose (linear)

amylopectin (occasional branching)

Cellulose

β-D-glucose

Plant cell walls, rigid structure

Glycogen

α-D-glucose

Very, very branched

enables quick absorption for energy in muscles

Hydrolysis of carbohydrates

Starch, glycogen + enzymes, water → maltose → glucose

Cellulose + cellulase → usable fuel

Latent heat of fusion

Energy required to change a solid to a liquid

Volatility

Measure of how readily a substance will form a vapour

Primary standard

Must:

• High state of purity

• Accurately known formula

• Be stable/uncreative with atmosphere

• Cheap

• High molar mass

• Readily accessible

Melting point determination

Variations in mp can determine purity.

Impurity: interrupts regular lattice structure of compound, decreasing mp

Pure: 0.5 - 2 C range

Impure: 5+ C range

Thiele tube

Ensure sample is heated slowly to determine a more accurate mp range

1 C per min

Distillation

Functions based off different bp of compounds.

Most effective when compounds differ by at least 100 C

Distillation can be repeated multiple times to get a more pure distillate

Fractional distillation

Fractioning column - has beds/platforms in which vapour condenses, going back down the column. Separates compounds, making a more pure distillate and functioning the same as multiple boil-condense cycles

Starch indicator

Detects presence of Iodine.

brown → colourless/ox → reduced

In presence of iodine = dark blue

Methylene blue

Blue in presence of oxidising agent

Colourless in presence of reducing agent

Mass spectrometry

Splits particles to determine the molar mass of a compound, as well as information regarding arrangements of atoms within a molecule

Ionisation

Bombards a sample with high energy electrons, knocking some off, creating a positively charged ion

Only pos charged ions detected by mass spectrometer

Fragementation

Unstable molecular ion fragments, produces smaller ions

Base peak

Tallest peak in mass spectrometry

Molecular ion

Peak with largest mass-to-charge (m/z) value

Isotope effect

Smaller peak after molecular ion due to isotopes e.g ¹³C

Common Isotopes

⁷⁹Br ⁸¹Br, in ~ 50 50 ratio to one other

³⁵Cl ³⁷Cl

Infrared spectroscopy

Identifies functional groups through measuring energy absorbed by covalent bonds when exposed to infrared radition

Covalent bond vibration

Covalent bonds are always vibrating

When exposed to infrared radiation, this vibration changes

Non-polar bonds and molecules of only 2 of the same element will not absorb infrared radiation

Fingerprint region

Region below 1500 cm^-1 which is unique to each molecule. Not used in VCE study design

Factors affecting bond vibration energy

Strong bonds: more energy to change vibration, will vibrate at a higher frequency

Light atoms: more energy to change vibration, will vibrate at a higher frequency

NMR spectroscopy

Used to determine different “environments” surrounding each Carbon and Hydrogen in a molecule.

Basics of NMR

Nuclei have a “spin state”

Magnetic field applied aligns nuclei parallel/anti-parallel depending on their energy

As nucleus moves to low energy state, releases energy, which is then detected.

Shielding

Electrons/atoms surround nucleus will shield from magnetic field

Hence different chemical environments will release different energy levels

Chemical shift

Tetramethyl silane (TMS) taken as value 0

All other molecules measured in comparison to TMS

Pros of TMS

1 C and 1 H environment

Signal peak is well away from other peaks

Volatile, so can easily be separated

Inert compound

Low resolution H NMR

Number of peaks = number of unique hydrogen environments

Relative size of peak to one other determines ratio of hydrogens to each other

High-resolution H NMR

Peaks “split” according to number of hydrogens on adjacent carbons

Splitting pattern

0 H = 1 peak

1 H = 2 peaks

2 H = 3 peaks

3 H = 4 peaks

Surrounded by H attached to C in same environment, = multiplet, splitting up to 7 times

C NMR

Produces single peak, no splitting

Much larger chemical shift than H NMR

Stationary phase

Solid, liquid coating a solid, onto which components of a sample adsorb

Mobile phase

liquid, gas that flows through a chromatography system, moving materials along

Affinity

Attraction of a component to the stationary or mobile phase

Retention time

Time taken for component in a sample to elute

Resolution

Effective separation of components within a sample

Improved by increasing number of adsorb/desorb cycles

Chromatography

Technique used to separate components based on their polarity

Column chromatography

Chromatography done in a column, with components being collected from the bottom

Continuous mobile phase added throughout the process

High-performance liquid chromatography

1. Sample injected onto start of column as liquid

2. Eluent pumped through the column

3. Components separated through adsorption/desorption

4. As components exit column, usually detected by measuring the absorbance of UV light

Chromatogram

Makes graph based on retention time

Peak height corresponds to concentration of the component in the sample

HPLC quantitative analysis

Conc. of component = area under corresponding peak

Create a calibration curve, assists in finding concentration of unknown substance

Increasing resolution

Lower temp, components less soluble in mobile phase

Packing resin in column more tightly, components move slower

LC - MS

1. Inject sample in HPLC

2. As separated components leave the column, they are analysed by MS

3. Mass spectra are matched to identify the component

Optical isomer

Non-superimposable mirror image known as enantiomers

Do not have a plane of symmetry

Extraction

Process of moving a substance from one phase to another, generally to isolate a specific component

2-amino acid

Amino + carboxylic acid group attached to same carbon

Type of amino acid found in the body

Zwitterion

Molecule that contains both positively and negatively charged groups, with a net charge of 0

Substrate

Reactants in an enzymatic reaction

Active site

Area where substrate binds to an enzyme for a reaction to occur

Denaturation

Enzyme/protein loses its 3D shape

Only primary structure, disulfide bridges remain

Competitive inhibitor

Inhibitor that binds to the active site of an enzyme in place of the substrate

Stereoisomer

Atoms are connected in the same order, but are oriented differently in space

Chiral

Asymmetrical molecule: chiral

Symmetrical molecule: achiral

Carbon bonded to 4 different atoms or groups of atoms

A molecule will form enantiomers if it has a chiral centre

Polarised light interactions

Enantiomers will rotate polarised light.

If light is rotated clockwise, it is the + enantiomer

If light is rotated anticlockwise, it is the - enantiomer

Synthetic formed stereoisomer

Optically active, produced 50:50 mixture of 2 enantiomers (aka racemic mixture)

Biological formed stereoisomer

1 stereoisomer formed

May function for a specific biological task where the other enantiomer is not useful, hence only one is produced

Solvent extraction

2 layers created through a suitable solvent + immiscible solvent e.g. opposite polarities

Funnel closed + shaken, allows two layers to mix

Mixture with varying polarities will be separated, allowing scientists to isolate certain components

Acid-base solvent extraction

e.g. with Salicylic acid

Non-polar organic solvent (hexane) added to dried plant to dissolve salicylic acid

NaOH _(aq) is added, forming a salicylate salt

--—→ contains charged -COO^- group, dissolving in polar layer

can then be extracted, HCL may be added to convert back to salicylic acid

Primary structure

Amino acids covalently bonded with peptide/amide links

Secondary structure

Folding of polypeptide chain due to hydrogen bonding

α-helix: hydrogen bonds between peptide bonds that are 4 amino acids apart

β-pleated sheets: two section of same peptide line up and held together in a sheet-like structure

Tertiary structure

3D structure of protein, referred to as its conformation.

Interactions between R-groups

e.g. ionic, disulfide bridges, hydrogen

Quaternary structure

Proteins with 2 or more folded peptide chains combined

Bonds: hydrogen bonding, disulfide links, ionic attractions