Organic chemistry Flashcards
What are aliphatic hydrocarbons?
Straight or branched carbon backbone
What are alicyclic hydrocarbons?
Carbon atoms in a ring
What are aromatic hydrocarbons?
Delocalised ring
What is a general formula?
A formula for all members of a homologous series that involves algebra. e.g. alkanes are CnHn+2
What is a displayed formula?
A drawing of the molecule
What is a structural formula?
A formula that gives the minimum detail for the arrangement of atoms in a molecule. An example would be CH3(CH2)2CH3 for butane
What is an empirical formula?
A formula that shows the smallest integer ratio of atoms in the compound (e.g. H2O2 = HO)
How do skeletal formulae work?
A zigzag where each corner represents an atom in the carbon backbone
What are structural isomers?
Compounds with the same molecular formulae but different structural formulae
What are the three ways structural isomers can happen?
Alkyl groups in different places (different carbon backbone)
Functional groups in different places (e.g. primary vs secondary alcohols)
Different functional groups (e.g. aldehydes vs ketones)
What are stereoisomers?
Compounds with the same structural and molecular formulae, but with a different arrangement of atoms in space (different displayed formulae). This is usually due to a double bond preventing the atoms from rotating freely
What is homolytic fission?
When a covalent bond breaks and each electron goes to a different atom, forming two highly reactive radicals (atoms with an unpaired electron)
What is heterolytic fission?
When a covalent bond breaks and both electrons go to the more electronegative part, forming a positive and a negative ion
What does a curly arrow in a diagram represent?
The movement of two electrons
What is a sigma bond?
A type of covalent bond where electron orbitals of two atoms overlap end-to-end. Sigma bonds are generally stronger than pi bonds because the extent of overlap is maximum. Single bonds consist of a single sigma bond.
What is a pi bond?
A type of covalent bond where the lobes (ends) of two electron orbitals overlap. Double bonds consist of a sigma bond and a pi bond.
Describe the bonding in an alkane
Alkanes contain sigma bonds (C-H and C-C). C and H have similar electronegativity values, meaning alkanes are non-polar
Why do alkanes’ boiling points increase as the chain length increases?
The surface area of contact between molecules increases, increasing the number of induced dipole-dipole forces
Why do branched alkanes have lower boiling points?
The surface area of contact between molecules is lower
Why do alkanes have low reactivity with many reagents?
All the covalent bonds in alkanes have low electronegativity and high bond enthalpy
What are the types of combustion of alkanes?
Complete (producing CO2 and water), and incomplete (producing CO2, water, carbon and carbon monoxide)
Describe the bonding in alkenes
Double C=C bonds which contain a sigma and a pi bond. The pi bond restricts rotation around the C=C double bond
Why do alkenes have a trigonal planar shape?
Each carbon atom has 3 areas of electron density, the double bond and the two C-H single bonds. The negatively charged areas repel, forming bond angles of 120.
What are electrophiles?
Species which accept electron pairs
Why are alkenes more reactive than alkanes?
The high density of the C=C bond attracts electrophiles
What is a saturated hydrocarbon?
A hydrocarbon with only single bonds, such as an alkane
Why do plastics remain chemically unchanged in the environment for hundreds of years?
They are saturated organic compounds, meaning they are very stable
How are plastics disposed of?
Landfill, combustion, reusing, recycling, using them as organic feedstock
Describe the combustion of a plastic
Since plastics are organic, they can be burnt. Their combustion releases carbon dioxide, which is a greenhouse gas. Depending on the type of plastic, other gases such as HCl can be made, which can be removed using gas scrubbers or a base such as CaO. Plastics can be burnt in power stations to generate heat and produce electricity
Describe the recycling of plastic
Plastics are sorted into different types, which is labour intensive. They are then cleaned, melted down and reshaped into new products. These new products are often of worse quality, and only 7% of plastic is recycled
What is a primary alcohol?
An alcohol where the oxygen in the -OH group is bonded to a C with only one other C attached
How do you tell if an alcohol is primary, secondary or tertiary?
Look at how many carbons are bonded to the carbon bonded to the -OH group (1 = primary etc.)
Why do alcohols’ boiling points increase as the chain length increases?
The surface area of contact between molecules increases, increasing the number of induced dipole-dipole forces
Why do alcohols have higher boiling points than their corresponding alkanes?
There are hydrogen bonds between molecules, caused by the oxygen atom
What is volatility?
The tendency of a substance to evaporate at room temperature
Why are alcohols less volatile than alkanes?
Hydrogen bonds
Why do alcohols become less soluble as chain length increases?
The aliphatic chain cannot form hydrogen bonds
What is reflux?
Constant boiling and condensing of a reaction mixture. This ensures that the reaction completes as much as possible without losing reactants or products to the air
What happens when you try to oxidise a tertiary alcohol?
Nothing
How are esters named?
First part: Name of alkyl chain attached to -OH on alcohol
Second part: Carboxylic acid stem name + “-oate”
Describe the reactivity of haloalkanes
There is a difference in electronegativity between halogens and carbon, so haloalkanes are polar. The positive carbon atom is attacked by nucleophiles (species with full or partial negative charge which donate electron pairs)
Describe nucleophilic substitution of a haloalkane
The two unpaired electrons from the nucleophile form a bond with the slightly positively charged carbon atom, breaking the carbon-halogen bond.
What is hydrolysis?
A type of nucleophilic substitution where water provides the OH- ions which act as nucleophiles.
What determines the rate of hydrolysis?
The bond enthalpy of the carbon-halogen bond. This decreases as the halogen gets bigger, meaning that iodoalkanes hydrolyse the fastest
Describe hydrolysis using aqueous alkali
When a haloalkane is heated under reflux with hydroxide ions, an alcohol is made. This reaction is faster than hydrolysis with water
What are chlorofluorocarbons?
Haloalkanes containing fluorine and carbon. They are inert due to the high bond enthalpies of the C-Cl and C-F bonds. They are used for refrigeration and fighting fires.
How do chlorofluorocarbons damage the ozone layer?
When the CFCs reach the stratosphere, they are exposed to UV, forming radicals which decompose ozone into oxygen
What is the difference between electrophilic substitution and electrophilic addition?
Electrophilic substitution involves an atom or group being lost from the molecule
Describe electrophilic substitution of benzene
Benzene donates an electron to the electrophile, breaking the delocalised ring. An unstable positive ion forms. H+ is lost, and the delocalised ring is reformed
What is a halogen carrier?
A catalyst that accepts a lone pair of electrons from a halogen atom on an electrophile, increasing the polarisation in the molecule. These include aluminium halides, iron halides and iron
NaBH4 reduction reaction mechanism
H- ions from the NaBH4 donate an electron pair to the carbon and bond to it. This causes the oxygen to donate one of the electron pairs from the C=O bond to an H+ ion, forming a bond. The end result is that 2 hydrogens are added around the C=O bond. The same thing happens with KCN and acid, except the bottom H is replaced with CN.
How can you compare rates of hydrolysis of haloalkanes?
Putting silver nitrate solution in the mixture and seeing how long it takes for a precipitate to form and what colour it is
[PPQ] How does branching affect the boiling point of a molecule?
More branching means less surface contact between molecules, and therefore weaker London forces which require less energy to break
Describe the bonding in benzene
The p-orbitals of all carbons overlap to create a pi-system (two ring-shaped clouds of electrons, above and below the carbons). Thus all the bonds are the same, and the electrons are delocalised
Reaction of phenol with bromine water
Occurs because phenol is more reactive than benzene.
Phenol + 3Br2 => Tribromophenol + 3HBr
How do amino acids react with alkali?
The carboxylic acid group reacts, forming water and a salt
How do amino acids react with acids?
The amino group reacts and forms a salt of the conjugate acid
How do amino acids react with alcohols?
In the presence of a strong acid catalyst, an amino acid reacts with an alcohol to form an ester
What is a chiral carbon atom?
A carbon atom with 4 different groups attached to it, meaning the groups can be arranged in 2 different, non-superimposable ways. These molecules are called enantiomers
What happens when a molecule has N chiral centres?
It has 2^n optical isomers. If a molecule has 2 chiral centres, the isomers are:
- The original molecule
- The original but with one carbon mirrored
- The original but with the other carbon mirrored
- The original with both carbons mirrored
How do condensation polymers work?
The functional group on one monomer reacts with the functional group on another monomer to form a link, eliminating a small molecule (usually H2O or HCl)
How can condensation polymers be broken down?
Water molecules and H+ are added, and the links are broken (hydrolysis). Polyamides hydrolyse easily with an acid and polyesters hydrolyse easily with a base
How do dicarboxylic acids and diamines react?
Each molecule forms CONH links with 2 other molecules, releasing water and forming a polyamide
How do dicarboxylic acids and diols react?
Each molecule forms COOH (ester) links, forming a polyester
What is the carbonyl functional group?
C=O
Reaction of hydrogen cyanide with carbonyl compounds
Nucleophilic addition reaction, producing hydroxynitriles
How do you test for the presence of a C=O group in aldehydes and ketones?
Add 2,4-DNP (Brady’s reagent) dissolved in methanol and concentrated sulfuric acid, and a bright orange precipitate will be formed. This precipitate is a derivative of the compound and has a unique melting point. If you crystallise the precipitate and measure the melting point of the crystals, you can work out the compound
How do you use Tollens’ reagent to test for an aldehyde?
Tollens’ reagent is a solution of silver nitrate in aqueous ammonia. When heated in a test tube, the aldehyde is oxidised and the silver ions are reduced, forming a silver mirror. This does not happen with ketones because they cannot be oxidised
What are acyl chlorides?
Like carboxylic acids but with the functional group -COCl instead of -COOH. Their names end in “-oyl chloride” and they’re made by reacting carboxylic acids with thionyl chloride (SOCl2)
How do acyl chlorides react with water?
Vigorous reaction with cold water, producing a carboxylic acid. All 4 reactions of acyl chloride are nucleophilic addition-elimination reactions
How do acyl chlorides react with alcohols?
Vigorous reaction at room temperature, producing an ester
How do acyl chlorides react with ammonia?
Violent reaction at room temperature, producing a primary amide
How do acyl chlorides react with amines?
Violent reaction at room temperature, producing a secondary amide
How do acyl chlorides react with phenol?
They produce an ester (e.g. phenyl ethanoate) and hydrochloric acid. This is faster than using carboxylic acids, which react very slowly with phenol
What are amines?
Organic derivatives of ammonia with the hydrogen atoms replaced by organic groups. Whether the amine is primary, secondary, tertiary or a quaternary ammonium ion depends on how many H atoms have been substituted. Amines are bases because the lone pair of electrons on the nitrogen can accept protons
How can amines be made from haloalkanes?
By heating a haloalkane with an excess of ammonia dissolved in ethanol. This is unpredictable and will produce a mixture of the 4 types of amine.
How are aromatic amines made?
Heat a mixture of an aromatic nitro compound, tin, and concentrated hydrochloric acid under reflux, making a salt. Then add sodium hydroxide to get the aromatic amine.
What are the reagents for acylation and alkylation?
AlX3 + RX
X is a halogen (usually chlorine), and X is whatever you’re adding (CH3 or CH3CO)
What are the concerns raised by the use of polymers?
Incinerating them produces toxic gases, and if not incinerated they stay in nature for thousands of years
How are degradable polymers developed?
Polymers with C=O bonds are photodegradable (into CO2 and H2O). Some are also readily degradable by hydrolysis at pH 7
Formation of an aliphatic amine
Haloalkane + anhydrous ethanol + NH3 => Halide ion + Amine salt
Halide ion + amine salt + OH- => Amine + H2O + Halide ion
What is the problem with the reaction between haloalkanes and ammonia?
The reactants can react with the products
How can you control the major product of the reaction between haloalkanes and ammonia?
Excess ammonia means the major product is the primary amine
Excess haloalkane means the major product is the quaternary salt
Reduction of nitriles
A reducing agent turns the -C≡N group into -C-NH2 Agents: anhydrous LiAlH4: 4[H] anhydrous Na (alcohol): 4[H] Ni (catalyst): 2H2
Preparation of aromatic amines
Nitrobenzene + Sn + conc HCl under reflux => Phenylamine
ArNO2 + 6[H] + HCl => ArNH3+ + Cl- + 2H2O
ArNH3+ + Cl- + NaOH => ArNH2 + NaCl + H2O
How are solids and liquids separated after a reaction?
Solids are normally separated by filtration and liquids are separated by simple, fractional or steam distillation
How are solids and liquids purified after a reaction?
Liquids are normally purified by distillation and solids are purified by recrystallisation
How can the product of a reaction be identified?
Melting/boiling points, simple tests, NMR
