Chemistry SAC 4 Flashcards: Organic Chemistry

For memory

Diversity of carbon

• All 4 valence electrons available for bonding

• Forms chains & rings via single, double, or triple bonds

• Bonds with non-metals (eg. O, N, S, P, Cl)

• Forms strong, stable bonds taking lots of energy to break

Saturated hydrocarbons

A molecule which only contains single carbon-carbon bonds between atoms

Unsaturated hydrocarbons

A molecule which contains at least one double/triple bond between atoms

Bond energy

The energy (kJ) required to break 1 mole of covalent bonds in gaseous state

• The higher bond energy, the higher bond strength and stability

• The relative strength of C-C bonds explains the frequency of carbon chains on Earth.

Organic molecule representation

• Molecular: indicates the number & type of each atom present in a molecule (C4H8O)

• Structural: shows the location of atoms relative to each other, and the number and location of covalent bonds

• Semi-structural: indicates the connections in compound’s structure without showing 3D arrangement of atoms

• Skeletal: a shorthand version of structural formula, showing only C-C bonds and functional groups

Isomers

Molecules with the same number & type of atoms but different arrangements:

• Chain: different chain lengths due to branching

• Positional: branch/functional group is moved

• Stereoisomer: when groups around an atom are arranged differently

Homologous series

A family of organic molecules that have similar structures and properties, general formula, a pattern in physical properties.

Alkanes (and naming)

Saturated hydrocarbons (single C-C) with the general formula: C_nH_2n+2

Naming:

• Named with a prefix of # Cs and the suffix -ane

• Side branches are named using a prefix and -yl

• Use prefixes di, tri for multiple branches of one type

• Branch position is found by numbering each main chain C

• Give branches lowest number possible and list branches in alphabet order

• Eg. 5-methylpropane

Cycloalkane

Carbon atoms which form rings, and only single C-C bonds are present, with the general formula: C_nH_2n

• Eg. Cyclohexane (C₆H₁₂)

Alkenes (and naming)

Unsaturated hydrocarbons (double C-C) with the general formula: C_nH_2n

Naming:

• Names end in -ene

• 2Hs are lost for each C-C double bond

• Double bond position must be given the LOWEST number —> insert position before -ene

• Eg. 3,3-dimethylpent-1-ene

Degree of unsaturation

• Refers to the number of double bonds/rings in a molecule

• Calculated by: ([(2 * no of Cs)+2] - no of Hs) / 2

Benzene

An unsaturated 6C ring (C₆H₆):

• Fourth electron of each C becomes delocalized and shared by all Cs (1 ½ bonds)

• When bonded to an alkyl/functional group, it is known as a phenyl functional group (C₆H₅^-)

Haloalkanes (and naming)

Alkanes with one or more H atoms replaced by a halogen atom (Cl, I, Br, F) —> this results in a polar bond

Naming:

• Prefixes (fluoro, chloro, bromo-)

• Location must be given (eg. 4-bromo)

• Numbers must be as low as possible

• For multiple halogens use dichloro, trichloro, etc.

Types of alcohols

Contains the -OH group (hydroxyl), classified based on structure:

• Primary: the C bonded to -OH group is bonded with one alkyl chain (R group)

• Secondary: the C bonded to -OH group is bonded with two alkyl chains

• Tertiary: the C bonded to -OH group is bonded with three alkyl chains

• NOTE: The polar bond from OH allows for H bonding and CO bond makes it reactive

Naming alcohols

• Suffix with -ol (eg. ethanol)

• In some cases, the prefix hydroxy- is used

• Insert a number before -ol to indicate position of -OH groups, and give the lowest number possible

• For multiple alcohol groups use diol, triol, tetraol, etc.

Types of amines

Contains the -NH2 group (amino), classified based on structure:

• Primary: N is bonded to one alkyl chain and two Hs

• Secondary: N is bonded to two alkyl chains and one H

• Tertiary: N is bonded to three alkyl chains and no Hs

• Only primary amines have to be known

Naming amines

• Suffix with -amine

• Use numbers to determine amino group position, and lowest number possible

Carbonyl group

A C double bonded to an O:

• Polar

• Angle between bonds is 120 degrees

• Includes amides, aldehydes, ketones, carboxylic acids, and esters

Aldehydes

Contains a carbonyl group located at one end of an alkyl chain

• Written as -CHO in semi-structural formulas

• The carbonyl is always given the 1st position

• Suffix is -al and sometimes the prefix oxo- (eg. ethanal)

Ketones

Contains a carbonyl group bonded to two other alkyl chains (never at the end)

• Written as -CO- in semi-structural formulas

• Suffix is -one and sometimes the prefix oxo-

• Carbonyl group position is always indicated

Carboxylic acids

Contains a carbonyl group (-COOH), with the C bonded to a hydroxyl group

• Written as -COOH in semi-structural formulas

• The C in the carboxyl group is always at the end of the chain, hence its position is always 1

• Suffix is -oic acid

Amides

Contains a amide group (-CONH2) bonded to the C of the carbonyl group

• Usually derived from carboxylic acids

• Primary amides have N bonded to one alkyl chain, while in secondary and tertiary it is bonded to two and three

• Suffix is -amide

Esters

Formed from condensation reactions (H2O) between an alcohol and carboxylic acid.

• Eg. Ethanoic acid + Methanol —> Methyl ethanoate + water

• Written as -COO or -OCO- in semi-structural formulas

• Two part suffixes: -yl suffix derived from the alcohol reactant, -oate suffix derived from the carboxylic acid.

IUPAC Nomenclature (priority)

Use suffixes for higher priority and start chain there, use prefixes for lower priority

1. Carboxylic acid: -oic acid

2. Aldehyde: -al, oxo-

3. Ketone: -one, oxo-

4. Hydroxyl: -ol, hydroxy-

5. Amino: -amine, amino-

6. Alkene: -ene, -en-

7. Halogen: halo- (eg. fluoro-)

Physical properties of homologous series

Factors such as molecule size, molecule shape, and type of bonding can affect compounds’ melting points, boiling points, viscosities.

Properties of alkanes

• Non-polar molecules, hence only weak dispersion forces can form

• As chain length increases, melting & boiling points increase due to more dispersion forces as there are more contact points

• The strength of temporary dipoles increase as chain length increases

• As linear molecules pack more closely with more SA in contact compared to branched molecules, dispersion forces are stronger in linear molecules.

Viscosity

Defined as the resistance to pouring, and depends on forces of attraction between molecules

Properties of alkenes

• Non-polar molecules, hence can only form dispersion forces

• Boiling and melting points of alkenes are similar to alkanes of a similar length

Properties of haloalkanes

• Polar molecules, hence dipole-dipole and dispersion forces can form

• As dipole-dipole forces are stronger than dispersion forces, BP and MP is usually higher

• A chain length increase also leads to increased strength of bonds

Properties of alcohols

• Polar molecules, and can form H bonds due to the O atom present

• Hence MP, BP, and viscosity is higher than alkanes of the same length due to the higher strength of H bonds.

• Primary alcohols have higher BPs and MPs than secondary/tertiary alcohols:

  • This is due to the hydroxyl position which does not restrict the formation of H bonds as much

Properties of amines and amides

• H bonds form between amines and amides, hence this leads to higher MPs, BPs, and viscosity than hydrocarbons of a similar size

Properties of carboxylic acids

• Carboxylic acid can form hydrogen bonded dimers, hence leading to higher MP and BP than alcohols

• Dimers have double the molar mass of the carboxylic acid, hence resulting in stronger dispersion forces between dimers.

• This process is called dimerisation

Properties of aldehydes, ketones, and esters

• These compounds contain a C-O double bond, resulting in polar molecules

• Hence they can form dipole-dipole bonds but not H bonds due to no O-H bond present.

• Their BPs and MPs are higher than alkanes but lower than alcohols.

Combustion reactions

• Alkanes, alkenes and alcohols readily undergo combustion to produce CO2 and H2O

• Eq: CH4(g) + 2O2(g) —> CO2 (g) + 2H2O(l)

Substitution of alkanes

• Substitution: when another replaces an atom/functional group

• Alkanes undergo substitution with halogens under UV light to produce haloalkanes and hydrogen halides

• Eq: CH4(g) + Cl2(g) —UV light—> CH3Cl(aq) + HCl(aq)

• Any H atom can be substituted and replaced one at a time, allowing it to react multiple times.

Substitution of haloalkanes

• Due to polarity, the C atom carries a d+ charge and react with negatively-charged particles such as OH- or d- N in NH3.

Nucleophile

A negative particle that can share a pair of electrons with a d+ carbon (eg. OH-, NH3, H2O)

Water as a nucleophile

As water is a weak nucleophile, it requires a catalyst/heat to react with haloalkanes

Different haloalkane substitution reactions

• OH: Haloalkanes + OH —> alcohol + salt

• Eq: NaOH(aq) + CH3Cl (aq) —> CH3OH + NaCl(aq)

• NH3: Haloalkanes + NH3 —> amine + hydrogen halide

• Eq: C2H5Cl + NH3 —> CH3CH2NH2 + HCl

• Water: Haloalkanes + H2O —> alcohol + hydrogen halide

• Eq: H2O(l) + CH3Cl(aq) —> CH3OH(aq) + HCl(aq)

Addition reactions of alkenes

Addition reactions:

• Two molecules combine to form one product

• The C=C double bond becomes C-C single bond

• An unsaturated compound becomes saturated

• The atoms are added across the double bond

Alkenes + hydrogen gas

• This reaction is called hydrogenation (high activation energy)

• Under the presence of a solid catalyst (Ni, Pt), alkenes react with H2 to form alkanes

• Eq: CH2CH2 + H2 —Ni—> CH3CH3

Alkenes + halogens

• This reaction does not require a catalyst

• Halogens such as Br2, Cl2 can be added across a double bond

• Eq: CH2CH2 + Br2 —> CH2BrCH2Br

Bromine test (Br2)

• This test is used to test for double bonds

• When Br2 is added across a double bond, the solution goes from reddish-brown to colourless (final haloalkane)

Alkenes + hydrogen halides

• Hydrogen halides are added across a double bond to form a haloalkane

• If symmetrical alkene (eg. but-2-ene): only one product is formed

• If asymmetrical alkene (eg. but-1-ene): two different isomers are possible

Alkenes + water

• Water added across a double bond produces an alcohol

• Under solid phosphoric acid and high temps (300C), this reaction can proceed

• Eq: CH2CH2 + H2O —300C & H3PO4—> CH3CH2OH

• Multiple isomers can form if the alkene is asymmetrical

Oxidation of alcohols

• Alcohols can be oxidised to aldehydes, ketones, and carboxylic acids using strong oxidising agents.

• Oxidation is the process of breaking C-H bonds and replacing them with C-O bonds, hence more C-O bonds = more oxidised

Oxidation of primary alcohols

• Primary alcohols: the carbon attached to OH group is connected to one carbon

• When oxidised, alcohols convert into aldehydes and then carboxylic acids, but sometimes the intermediary stage is skipped

• Ethanol —KMNO4/H+—> Ethanal —KMNO4/H+ & heat—> Ethanoic acid

Oxidation of secondary alcohols

• Secondary alcohols: the carbon attached to OH group is connected to two carbons

• When oxidised, alcohols convert into ketones

• Propan-2-ol —K2Cr2O7/H+ & heat—> Propanone

Oxidation of tertiary alcohols

• Tertiary alcohols: the carbon attached to OH group is connected to three carbons

• These cannot undergo oxidation as there are no C-H bonds to give electron pairs for the conversion of -OH to =O group.

Oxidants of alcohols

• Dichromate: Cr2O72- is orange, while Cr3+ is green

• Permanganate: MnO4- is purple, while Mn2+ is colourless

• Colour changes can indicate if an oxidation reaction has occurred

Ionisation of carboxylic acids in water

• Carboxylic acid + water —> -oate ions + hydronium ions

• Eq: CH3COOH + H2O —> CH3COO- + H3O+

Formation of esters (esterification)

• Esters are formed from condensation reactions between an alcohol + carboxylic acid, known as an esterification reaction

• The H in the hydroxyl group reacts with OH from the cabroxyl group, forming H2O

• This reaction can only occur under concentrated H2SO4 and heat.

• Eg: ethanoic acid + ethanol —> ethyl ethanoate + water

Hydrolysis of esters

• Hydrolysis is the reverse reaction of condensation, hence H2O can break ester bonds and produce a carboxylic acid + alcohol.

• Hydrolysis is catalysed using a dilute acid or an alkali

Hydrolysis of esters (dilute acid)

• Products are an alcohol and a carboxylic acid

• Eq: ethyl propanoate + H2O —> propanoic acid + ethanol

Hydrolysis of esters (dilute alkali)

• Products are a salt of the carboxylic acid and an alcohol

• The salt can be converted to a carboxylic acid using a dilute acid

• Eq: ethyl propanoate + H2O —NaOH—> sodium propanoate + ethanol —> propanoic acid after acidification

Triglyceride

A fat molecule consisting of three long hydrocarbon chains attached to a three-carbon backbone through ester bonds.

Transesterification

• This reaction occurs when triglycerides react with alcohols —> the alcohol R group swaps positions with the R group attached to the -O- of the ester.

• Eq: triglyceride + methanol —KOH—> three fatty acid esters + glycerol

Biodiesel formation

Biodiesel is formed by triglycerides reacting with an alcohol in the presence of KOH catalyst, as the fatty acid esters are biodiesel.

Reaction pathways

• A series of steps to convert starting materials (alkanes, alkenes) into desired products

Alkenes to alcohols

• Eg: ethanol from ethene

  • ethene + HCl —> chloroethene + OH —> ethanol

  • OR ethene + H2O —H3PO4—> ethanol

Alkanes to carboxylic acids

• Eg: propane to propanoic acid

  • propane + Cl2 —UV—> 1-chloropropane + OH —> propan-1-ol —Cr2O72—> propanoic acid

Alkanes + alkenes to form esters

• Ethene + H2O —> ethanol

• Propane + Cl2 —UV—> 1-chloropropane + OH —> propan-1-ol —Cr2O72—> propanoic acid

• Ethanol + propanoic acid —H2SO4—> ethyl propanoate

Summary of reaction pathways

• Alkanes: addition of halogen to form haloalkanes

• Alkenes:

  • Addition of H2 & catalyst to form alkanes

  • Addition of catalyst to form polyethane

  • Addition of hydrogen halides & catalyst to form haloalkanes

  • Addition of water to form alcohols

• Haloalkanes:

  • Addition of OH- ions to form alcohols

  • Addition of NH3 to form aminoalkanes

• Alcohols:

  • Oxidation using Cr2O72- to form carboxylic acids

  • Addition with carboxylic acids to form esters

• Carboxylic acids:

  • Addition with alcohol to form esters

Yield

The efficiency of processes that involve chemical reactions found by calculations.

Actual yield

The amount of desired product formed in the reaction

Theoretical yield

The mass of the product that can be formed if the limiting reactant reacts according to stoichiometric ratios —> assumes 100% efficiency

Percentage yield

Measures a chemical reaction’s efficiency by comparing actual yield to theoretical yield as a proportion.

• % yield = actual / theoretical * 100

• Use limiting reagent to find theoretical yield

Overall percentage yield

• This is the percentage yield of EACH step multiplied together

• Overall % yield = actual1 / theoretical1 x actual2 / theoretical2 × 100%

Why actual yield < theoretical yield?

• Slow reaction rate, hence reaction may not proceed in the time available

• Reaction reaches equilibrium rather than completion

• Loss of reactants/products during transfer between containers

• Unwanted side reactions occurring, hence forming unwanted products.

Atom economy

• The proportion of atoms in reactants that become useful products —> measures waste produced

• Formulas:

  • Molar mass of useful product / molar mass of all reactants * 100

  • Molar mass of useful product / molar mass of all products * 100

  • These two formulas are interchangable as total mass of products = total mass of reactants

Green Chemistry principles

• Use renewable feedstocks (raw materials)

• Catalysts

• Designing safer chemicals

Renewable feedstocks

These are beneficial as they are not as finite as fossil fuels, and some are also biodegradable, meaning they do not persist in the environment as wastes

Catalysts

• Allows reactions to proceed at low temperatures, reducing costs and saving energy

• Increase reaction rates hence more yield in a shorter time

• Not consumed directly so they can be continuously reused

Safe chemicals

• These are chemicals which have low impact on humans and the environment

• Eg. toxic chemicals such as perfluoroalkyls used in firefighting foam have been found to harm both environment and humans, hence replacements must be found.

Condensation reaction

These endothermic reactions occur when two functional groups react and water is formed as a by product.

Types of polymers

• Homopolymer: contains one type of monomer

• Copolymer/Heteropolymer: contains two or more different momoners

Proteins

• These are polymers of amino acids

• The general formula of amino acids is H2NCHRCOOH (variable R group —> defines properties of protein)

• Amino acids in proteins are called 2-amino acids as the main functional groups are attached to the number 2 carbon

pH vs protein charge

• Low pH: the amine group becomes NH3+, meaning it has a positive charge

• Neutral pH: known as a zwitterion_, both amine and carboxyl group are charged positively and negatively respectively (hence neutral)

• High pH: the carboxyl group becomes COO-, meaning it has a negative charge.

R groups’ properties

• Non-polar

• Polar

• H+ acceptors (basic)

• H+ donors (acidic)

Peptide bond

These bonds form when two amino acids combine through a condensation reaction.

Types of peptides

• Dipeptide: two amino acids bonded together

• Tripeptide: three amino acids bonded together

• Polypeptide: many amino acids bonded together

• Protein: >50 amino acids bonded together + polypeptide folding

Polypeptide ends

• The free amino group is called the N-terminus (on the left)

• The free carboxyl group is called the C-terminus (on the right)

Carbohydrates

These biomolecules are made from the elements C, H and O, with the general formula CxHyOz.

Types of saccharides

• Monosaccharide: a subunit of a carbohydrate, generally white, sweet-tasting, and water-soluble

• Disaccharide: two monosaccharides bonded together through a condensation reaction

• Polysaccharide: long polymers of monosaccharides, often water insoluble and tasteless

• The link between monosaccharides is called an ether group, also known as a glycosidic link

Monosaccharides

• C6H12O6 isomers:

  • Glucose (has 2 stereoisomers)

    • Alpha-glucose: found in starch and glycogen

    • Beta-glucose: found in cellulose

  • Galactose (not found free in nature)

  • Fructose

Disaccharides

• Occurs when two monosaccharides undergo a condensation reaction, forming an ether group/glycosidic link and water

• Maltose (used as a sweetener)

• Sucrose (table sugar)

Polysaccharides

• Starch: produced in plants through the actions of enzymes —> used for energy storage

  • Amylose is linear while amylopectin is branched

  • Amylopectin may be more soluble than amylose as -OH groups are more exposed due to branching

• Glycogen: used in animals for energy storage —> a branched polymer of glucose, more so than amylopectin.

Lipids (fats & oils)

Non-polar food molecules used for energy storage —> triglycerides are major parts of lipids.

Triglycerides

• Produced through condensation reactions between three fatty acids and glycerol, producing water and a triglyceride containing three ester links (-COO-)

• Eq: 3 Fatty acids + glycerol —> Triglyceride + 3H2O

Types of fatty acids

• Saturated: fatty acids only contain single C-C bonds

• Monounsaturated: fatty acids contain one C=C bond

• Polyunsaturated: fatty acids contain multiple C=C bonds.

Cellulose

A structural material in plants (cell wall) which provides structure and rigidity

Fats vs oils

• Fats: contains more saturated fatty acids (meaning more contact between side chains, increased dispersion forces, hence solid at room temp)

• Oils: contains more unsaturated fatty acids (meaning more double bonds & kinks, hence leading to liquid at room temp)

Hydrolysis

These exothermic reactions occur when large biomolecules are SPLIT through reactions with water molecules (essentially the opposite of condensation)

Hydrolysis of proteins

• A water molecule is added to each peptide bond (amide link)

  • C-N bond breaks

  • The -OH of water adds to the free C=O forming COOH group

  • The -H of water adds to the free NH forming NH2 group

  • The breaking of C-N bonds is sped up by enzymes, as without enzymes it would require harsh conditions such as 100C and 6M HCl

Hydrolysis of carbohydrates

• A water molecule is added to each glycosidic link

  • C-O bond breaks

  • The -H of water is added to the free O

  • The -OH of water adds to the free neighboring glucose

  • Amylase is used to catalyse starch hydrolysis, maltase is used to catalyse maltose hydrolysis, and cellulase is used to catalyse cellulose hydrolysis

Hydrolysis of lipids

• Lipids are insoluble in water, so molecules remain intact until they reach bile in the small intestine.

• Bile breaks lipids into globules and then small droplets which increases surface area, hence enabling hydrolysis.

• Lipase catalyses lipid hydrolysis by adding three H2O molecules to the ester links in the triglyceride

  • -OH of water is added to the CO of each fatty acid

  • -H of water is added to each O of glycerol

Digestion

Involves large numbers of enzymes through the digestive system, which breaks down different components of food.