Naming organic compounds Revision Notes

Displayed formulas show all atoms and bonds in a molecule, illustrating how atoms are connected.

Methane (CH₄) is the simplest alkane with one carbon atom bonded to four hydrogen atoms. The displayed structure shows a central carbon atom with four single bonds to hydrogen atoms arranged tetrahedrally.

Ethane (C₂H₆) is an alkane with two carbon atoms connected by a single bond, each carbon bonded to three hydrogen atoms. The displayed structure shows the C–C single bond and all C–H single bonds explicitly, reflecting the saturated nature of alkanes.

• Methane: CH₄, tetrahedral shape, all single C–H bonds.
• Ethane: C₂H₆, two carbons joined by a single bond, each carbon bonded to three hydrogens.
• All bonds in alkanes are single (sigma) bonds, making them saturated hydrocarbons.

Ethene (C₂H₄) is the simplest alkene containing a carbon-carbon double bond. The displayed formula shows two carbon atoms joined by a double bond and each carbon bonded to two hydrogen atoms.

The double bond consists of one sigma and one pi bond, restricting rotation and affecting reactivity.

The presence of the double bond classifies ethene as unsaturated, making it more reactive than alkanes.

• Ethene: C₂H₄, contains a C=C double bond.
• Each carbon atom forms two single bonds to hydrogen atoms.
• Double bond shown as two parallel lines between carbons in the displayed formula.
• The double bond influences molecular shape and chemical behaviour.

Ethanol (C₂H₅OH) is an alcohol with a hydroxyl (–OH) functional group attached to an ethyl group. Its displayed structure shows two carbon atoms bonded together, with one carbon bonded to the –OH group and the remaining bonds to hydrogen atoms.

Ethanoic acid (CH₃COOH) is a carboxylic acid containing a carboxyl group (–COOH). Its displayed formula shows a methyl group (CH₃) bonded to a carboxyl group, where the carbon is double bonded to one oxygen and single bonded to a hydroxyl group.

These functional groups determine the chemical properties of the compounds, such as ethanol’s solubility and ethanoic acid’s acidity.

• Ethanol: C₂H₅OH, with –OH group attached to a carbon atom.
• Ethanoic acid: CH₃COOH, with a carboxyl group consisting of C=O and –OH bonded to the same carbon.
• Displayed formulas show all bonds explicitly, including the polar O–H bonds.
• Functional groups influence physical and chemical properties.

Typical reactions involving these compounds produce characteristic products, whose displayed structures can be drawn.

For example, combustion of methane or ethane produces carbon dioxide and water:

CH₄ + 2O₂ → CO₂ + 2H₂O (balanced equation) with states (g) for gases and (l) for liquid water if condensed, but states are often omitted in organic combustion equations for simplicity. The products are CO₂ (carbon dioxide) and H₂O (water). The displayed structures of CO₂ show a linear molecule with two double bonds to oxygen atoms; water shows bent shape with two O–H bonds.

• Combustion of methane or ethane produces CO₂ and H₂O.
• Ethene undergoes addition reactions, e.g., with bromine (Br₂) to form dibromoethane:
• C₂H₄ + Br₂ → C₂H₄Br₂
• The product has single bonds only, with bromine atoms added across the double bond.
• Ethanol can be oxidised to ethanoic acid using acidified potassium dichromate(VI):
• C₂H₅OH + [O] → CH₃COOH + H₂O
• Displayed structures show the transformation of the –OH group to the carboxyl group.
• Understanding these products helps in predicting reaction outcomes and drawing their structures.

Organic compounds are classified according to their functional groups, which determine their chemical properties and reactivity. The names of these compounds often end with characteristic suffixes that indicate their type. Recognising these suffixes and understanding the molecular or displayed formulas allows chemists to identify the compound type accurately. This skill is fundamental in organic chemistry for naming, predicting reactions, and understanding properties.

• Suffixes in chemical names indicate functional groups.
• Molecular and displayed formulas show the arrangement and types of atoms.
• Classification aids in predicting chemical behaviour.

Alkanes are saturated hydrocarbons containing only single covalent bonds between carbon atoms. Their general formula is CₙH₂ₙ₊₂, where n is the number of carbon atoms. The suffix '-ane' in the name indicates an alkane.

For example, methane (CH₄) and ethane (C₂H₆) are alkanes.

Alkanes are relatively unreactive due to strong C–C and C–H single bonds and lack of functional groups.

• General formula: CₙH₂ₙ₊₂
• Only single bonds between carbon atoms
• Name ends with '-ane'
• Example: methane (CH₄), ethane (C₂H₆)

Alkenes contain at least one carbon–carbon double bond, making them unsaturated hydrocarbons. Their general formula is CₙH₂ₙ for molecules with one double bond. The suffix '-ene' indicates the presence of this double bond.

For example, ethene (C₂H₄) has a double bond between the two carbon atoms.

The double bond affects reactivity, making alkenes more reactive than alkanes, especially in addition reactions.

• General formula: CₙH₂ₙ (one double bond)
• Contains at least one C=C double bond
• Name ends with '-ene'
• Example: ethene (C₂H₄)

Alcohols are organic compounds containing one or more hydroxyl (–OH) functional groups attached to a saturated carbon atom. The suffix '-ol' indicates an alcohol.

For example, ethanol (C₂H₅OH) is an alcohol with the formula C₂H₆O.

Alcohols have different physical and chemical properties from alkanes and alkenes due to the polar –OH group, including higher boiling points and solubility in water.

• Contains hydroxyl (–OH) group
• Name ends with '-ol'
• Example: ethanol (C₂H₅OH)
• General formula for simple alcohols: CₙH₂ₙ₊₁OH

Carboxylic acids contain the carboxyl functional group (–COOH). Their names end with the suffix '-oic acid'.

For example, ethanoic acid (CH₃COOH) is a carboxylic acid commonly known as acetic acid.

Carboxylic acids are acidic due to the ability of the –COOH group to release H⁺ ions in solution, and they have distinctive properties such as sour taste and reactivity with bases to form salts.

• Contains carboxyl (–COOH) group
• Name ends with '-oic acid'
• Example: ethanoic acid (CH₃COOH)
• Acidic properties due to H⁺ ion release

Structural formulas represent the arrangement of atoms in a molecule showing how atoms are connected but do not explicitly show all bonds. They use chemical symbols and lines to indicate bonds between atoms.

Displayed formulas show every atom and every bond explicitly, including single, double, or triple bonds, making the bonding pattern clear. They help visualise molecular shape and functional groups.

Understanding these formulas is essential for recognising organic compounds, predicting their properties, and writing balanced chemical equations. Both formulas are used in organic chemistry to communicate molecular structure clearly.

• Structural formula: atoms and bonds shown simply, e.g., CH3CH2OH for ethanol.
• Displayed formula: all atoms and bonds shown, e.g., H–C–C–O–H with all hydrogens attached.

Alkanes are saturated hydrocarbons containing only single covalent bonds between carbon atoms. Their general formula is CnH2n+2.

Straight-chain alkanes have carbon atoms connected in a continuous chain without branches.

Each carbon forms four single covalent bonds (tetrahedral geometry), bonding to hydrogen or carbon atoms to satisfy the octet rule.

• Example: Butane (C4H10) structural formula: CH3–CH2–CH2–CH3.
• Displayed formula shows all C–H and C–C single bonds explicitly.
• Alkanes are relatively unreactive due to strong C–C and C–H single bonds.

Alkenes contain at least one carbon-carbon double bond (C=C) and have the general formula CnH2n for straight chains.

The double bond introduces unsaturation and affects reactivity and geometry (planar around the double bond).

But-1-ene and but-2-ene are isomers differing in the position of the double bond: but-1-ene has the double bond between C1 and C2; but-2-ene between C2 and C3.

• But-1-ene structural formula: CH2=CH–CH2–CH3.
• But-2-ene structural formula: CH3–CH=CH–CH3.
• Displayed formulas show the double bond explicitly as two lines between carbons.
• The presence of the double bond allows addition reactions, such as bromine addition.

Alcohols contain one or more hydroxyl (–OH) groups attached to a saturated carbon atom.

Their general formula is R–OH, where R is a hydrocarbon chain.

Propan-1-ol and propan-2-ol are isomers differing in the position of the –OH group: propan-1-ol has –OH on the first carbon; propan-2-ol on the second carbon.

• Propan-1-ol structural formula: CH3–CH2–CH2–OH.
• Propan-2-ol structural formula: CH3–CHOH–CH3.
• Butan-1-ol and butan-2-ol follow the same pattern with four carbons.
• Displayed formulas show all bonds including the O–H bond explicitly.
• Alcohols are polar due to the –OH group and can form hydrogen bonds, affecting boiling points.

Carboxylic acids contain the carboxyl functional group (–COOH), which consists of a carbonyl (C=O) and a hydroxyl (–OH) group attached to the same carbon atom.

Their general formula is R–COOH, where R is a hydrocarbon chain.

Carboxylic acids with up to four carbon atoms include methanoic acid (formic acid), ethanoic acid (acetic acid), propanoic acid, and butanoic acid.

• Example: Butanoic acid structural formula: CH3–CH2–CH2–COOH.
• Displayed formulas show the double bond between carbon and oxygen and the O–H bond explicitly.
• Carboxylic acids are acidic due to the ability to donate H+ from the –COOH group.
• They have higher boiling points than alcohols of similar molecular mass due to strong hydrogen bonding.

Esters are organic compounds formed by the condensation reaction between an alcohol and a carboxylic acid. This reaction involves the removal of a water molecule (H₂O) and the formation of an ester bond (–COO–).

The general reaction is: alcohol + carboxylic acid → ester + water.

For example, ethanol (C₂H₅OH) reacts with ethanoic acid (CH₃COOH) to form ethyl ethanoate (an ester) and water: C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O (balanced equation).

• Esterification is a condensation reaction releasing water.
• Requires an acid catalyst, commonly concentrated sulfuric acid, to speed up the reaction.
• Typically heated under reflux to increase yield.

Esters have the functional group –COO–, where the carbon atom is double bonded to one oxygen atom and single bonded to another oxygen atom that connects to an alkyl group from the alcohol.

In straight-chain esters, both the acid and alcohol parts are unbranched carbon chains, each with up to four carbon atoms.

Displayed formulas show all atoms and bonds explicitly, illustrating the connectivity and arrangement of atoms in the molecule.

• The ester functional group is shown as –COO– in displayed formulas.
• The alkyl group from the alcohol is attached to the oxygen atom of the ester group.
• The acyl group (R–CO–) comes from the carboxylic acid.

Common esters formed from straight-chain alcohols and carboxylic acids with up to four carbons include: methyl methanoate, ethyl methanoate, methyl ethanoate, ethyl ethanoate, methyl propanoate, ethyl propanoate, methyl butanoate, and ethyl butanoate.

Each ester is named by combining the alkyl group name from the alcohol and the acid name with the suffix '-oate'.

For example, ethyl ethanoate is formed from ethanol and ethanoic acid.

• Methyl acetate (methyl ethanoate): from methanol + ethanoic acid.
• Ethyl propanoate: from ethanol + propanoic acid.
• Ethyl butanoate: from ethanol + butanoic acid.

Consider the formation of ethyl ethanoate from ethanol and ethanoic acid.

Balanced equation: C₂H₅OH (l) + CH₃COOH (l) → CH₃COOC₂H₅ (l) + H₂O (l)

Displayed formula of ethyl ethanoate shows the carbon chain from ethanoic acid connected via the ester bond to the ethyl group from ethanol:

• CH₃–C(=O)–O–CH₂–CH₃
• The double bond between carbon and oxygen in the acyl group is clearly shown.
• The single bond between oxygen and the ethyl group is shown.

The esterification reaction requires heating under reflux with a strong acid catalyst, usually concentrated sulfuric acid, which acts both as a catalyst and a dehydrating agent to shift equilibrium towards ester formation.

Typical observations include the formation of a sweet-smelling liquid (the ester), which is often less dense than water and may form a separate layer if mixed.

The reaction is reversible; removal of water or excess reactants increases ester yield.

• Heat under reflux with concentrated H₂SO₄ catalyst.
• Smell characteristic fruity odour of esters.
• Use separating funnel to isolate ester from reaction mixture.