Unit 12 is about carbon compounds: how carbon builds chains and rings, how small groups of atoms attached to those chains shape behavior, and how the same chemistry builds the molecules in living things. By the end you should be able to name simple hydrocarbons, identify functional groups, recognize the four biomolecule classes, and predict products of basic organic reactions.
Read the big ideas first, then work through each topic note and try the checkpoint question before checking the answer.
Organic chemistry can feel like a new language, but most of it comes from rules you already know. Covalent bonding, polarity, intermolecular forces, and stoichiometry from earlier units all show up again here. This unit adds a naming system and a short list of reaction patterns.
Honors Chemistry Unit 12 covers organic chemistry at an introductory level. You learn why carbon forms so many compounds, how to name and draw alkanes, alkenes, and alkynes, and what isomers are. You then learn to recognize functional groups like alcohols, aldehydes, ketones, carboxylic acids, esters, ethers, and amines, and to connect them to properties like boiling point. The unit finishes with biomolecules (carbohydrates, proteins, lipids, nucleic acids) and the basic reaction types: substitution, addition, elimination, condensation, combustion, and polymerization. Exact content varies by school, and some courses skip or shorten this unit.
Carbon has four valence electrons, so it forms four covalent bonds. It bonds strongly to other carbons, which lets it form long chains, branches, and rings. That is why millions of organic compounds exist and why isomers with the same formula can have different structures.
A plain hydrocarbon chain is nonpolar and fairly unreactive. Adding a group like -OH or -COOH introduces polarity and hydrogen bonding, which raises boiling points and changes solubility. Chain length and branching matter too, since longer chains have stronger London dispersion forces. Molecules with the same functional group tend to react in the same ways.
Starch, proteins, fats, and nylon are all made by joining smaller molecules, often releasing water in a condensation reaction. Hydrolysis runs the process backward by adding water. Once you know these patterns, biomolecules and plastics stop looking like separate topics.
Every part of this unit comes back to one idea. The carbon skeleton and the functional groups attached to it decide a molecule's polarity, its intermolecular forces, and which reactions it can undergo. If you can read a structure, you can predict how the compound behaves.
Organic chemistry is the chemistry of carbon compounds, especially ones built on carbon-carbon and carbon-hydrogen bonds.
A functional group is a specific arrangement of atoms attached to a carbon skeleton that gives the molecule its characteristic properties.
Biomolecules are organic molecules found in or produced by living things.
Most organic reactions in this course fit a few patterns.
Organic chemistry is the chemistry of carbon compounds, especially ones built on carbon-carbon and carbon-hydrogen bonds. Carbon has four valence electrons, so it forms four covalent bonds and can link to other carbons in chains, branches, and rings. A few carbon compounds, like CO, CO, and carbonates, are traditionally classified as inorganic.
Hydrocarbons contain only carbon and hydrogen. Open-chain alkanes have only single bonds and follow . An open-chain alkene with one C=C double bond follows , and an open-chain alkyne with one C≡C triple bond follows . Rings and additional multiple bonds change these formulas. Alkanes are saturated, while alkenes and alkynes are unsaturated.
IUPAC names combine a prefix for the number of carbons in the parent chain (meth- 1, eth- 2, prop- 3, but- 4, pent- 5, hex- 6, hept- 7, oct- 8) with a suffix for bond type (-ane, -ene, or -yne). For an alkene or alkyne, choose a parent chain that contains the multiple bond and number it so that the multiple bond has the lowest possible locant. Then locate any branches, as in 2-methylpropane or but-2-ene.
Isomers share a molecular formula but differ in structure. Butane and 2-methylpropane are both .
Worked example. Find the formula and molar mass of heptane. Hept means 7 carbons and -ane means alkane, so H = 2(7) + 2 = 16, giving . Molar mass = 7(12.01) + 16(1.008) = 84.07 + 16.13 = 100.20 g/mol.
Check yourself. What is the molecular formula of propene, and is it saturated or unsaturated? Prop means 3 carbons and -ene means one double bond, so gives . The compound is unsaturated.
A functional group is a specific arrangement of atoms attached to a carbon skeleton that gives the molecule its characteristic properties. The hydrocarbon part is mostly nonpolar and unreactive. The functional group is where most of the chemistry happens.
Polar groups change physical properties. Groups that can hydrogen bond (-OH, -NH, -COOH) raise boiling points and make small molecules more soluble in water. Ethanol () boils at 78°C, but dimethyl ether () boils at -24°C even though both are . Ethanol has an O-H bond, so ethanol molecules can hydrogen bond to each other. Dimethyl ether has no O-H bond, so its molecules cannot hydrogen bond to each other, although its oxygen can accept hydrogen bonds from water.
Functional groups also predict reactions. Oxidizing a primary alcohol gives an aldehyde, and further oxidation gives a carboxylic acid. Oxidizing a secondary alcohol gives a ketone. A carboxylic acid plus an alcohol gives an ester plus water. Esters often smell fruity, which is why they show up in flavorings.
Watch the position of the C=O. In an aldehyde it sits at the end of the chain with an H attached. In a ketone it sits between two carbons. Naming patterns help you tell groups apart, so learn them alongside the structures in the table.
Check yourself. Propanone is a ketone and propanal is an aldehyde, and both are . Where is the C=O in each? In propanal, it is on carbon 1 at the end of the chain. In propanone, it is on carbon 2 in the middle.
| Functional group | Structure | Naming pattern | Example |
|---|---|---|---|
| Alcohol | -OH on a carbon | -ol | Ethanol, $CH_3CH_2OH$ |
| Aldehyde | C=O at chain end (-CHO) | -al | Ethanal, $CH_3CHO$ |
| Ketone | C=O between two carbons | -one | Propanone (acetone), $CH_3COCH_3$ |
| Carboxylic acid | -COOH | -oic acid | Ethanoic acid, the acid in vinegar, $CH_3COOH$ |
| Ester | -COO- linking two carbon groups | -oate | Ethyl ethanoate, $CH_3COOCH_2CH_3$ |
| Ether | R-O-R' | alkoxy- prefix in IUPAC names; simple common names end in ether | Dimethyl ether (methoxymethane), $CH_3OCH_3$ |
| Amine | -NH$_2$, -NHR, or -NR$_2$ | -amine | Methylamine, $CH_3NH_2$ |
| Amide | -CONH$_2$, -CONHR, or -CONR$_2$ | -amide | Ethanamide, $CH_3CONH_2$ |
Biomolecules are organic molecules found in or produced by living things. Four major classes are carbohydrates, proteins, lipids, and nucleic acids. Proteins and nucleic acids are polymers, and some carbohydrates, such as starch and cellulose, are polymers. Lipids are not true polymers.
Monosaccharides like glucose () join into disaccharides like sucrose and polysaccharides like starch, glycogen, and cellulose. Proteins are polymers of amino acids. Each amino acid has an amine group and a carboxylic acid group, and they link through peptide bonds, which are amide bonds. Nucleic acids (DNA and RNA) are polymers of nucleotides. A fat or oil consists mainly of triglycerides, each made of one glycerol molecule joined to three fatty acids by ester bonds. Saturated fatty acids have no C=C double bonds. Unsaturated fatty acids have one or more C=C double bonds. Cis double bonds bend the chain and often lower the melting point, which helps explain why many unsaturated fats are liquid at room temperature.
Many monomers join through condensation reactions. In common examples such as peptide-bond and glycosidic-bond formation, one water molecule is released for each new bond. Hydrolysis reverses these reactions by adding water to break the bond, which is what digestion does.
Worked example. Two glucose molecules join to form maltose. Find its molar mass. Two glucose = 2(180.16) = 360.32 g/mol. One water (18.02 g/mol) is released, so g/mol, matching .
Check yourself. How many water molecules are released when 4 amino acids join into a single chain? A chain of 4 amino acids has 3 peptide bonds, so the reaction releases 3 water molecules.
Most organic reactions in this course fit a few patterns. In substitution, one atom swaps for another, as in with UV light. In addition, atoms add across a double or triple bond, as in . Saturated alkanes cannot do addition because they have no double bond. Elimination removes atoms to form a double bond, as when ethanol loses water to become ethene. Condensation joins two molecules and releases a small molecule, usually water. In complete combustion, a hydrocarbon burns in enough oxygen to produce CO and HO. With limited oxygen, incomplete combustion can also produce CO or solid carbon.
Polymerization uses these patterns. Ethene molecules add to each other to make polyethylene, an addition polymer. Many common nylons and polyesters are condensation polymers. For example, nylon 6,6 is made by condensation polymerization.
A mechanism shows the step-by-step movement of electrons as bonds break and form. Electron-rich species (nucleophiles) are drawn to electron-poor atoms (electrophiles). Curved arrows always point from where electrons are to where they go.
Worked example. How many grams of CO form when 22.0 g of propane burns completely? The balanced equation is . Moles of propane = 22.0 g ÷ 44.10 g/mol = 0.499 mol. Moles of CO = 0.499 × 3 = 1.50 mol. Mass = 1.50 mol × 44.01 g/mol = 65.9 g CO.
Check yourself. Ethene reacts with H using a nickel catalyst. What type of reaction is this, and what is the product? This is an addition reaction called hydrogenation. The product is ethane, .
| Reaction type | What happens | Example |
|---|---|---|
| Substitution | One atom or group replaces another | $CH_4 + Cl_2 \rightarrow CH_3Cl + HCl$ |
| Addition | Atoms add across a double or triple bond | $C_2H_4 + H_2 \rightarrow C_2H_6$ |
| Elimination | Atoms are removed and a double bond forms | $C_2H_5OH \rightarrow C_2H_4 + H_2O$ |
| Condensation | Two molecules join and release a small molecule, usually water | Acid + alcohol $\rightarrow$ ester + $H_2O$ |
| Combustion | Hydrocarbon undergoes complete combustion in O$_2$ | $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$ |
| Term | Definition |
|---|---|
| Organic compound | A compound built on carbon, usually with C-C and C-H bonds. |
| Alkane | An open-chain hydrocarbon with only carbon-carbon single bonds and the general formula $C_nH_{2n+2}$. |
| Alkene | A hydrocarbon with at least one carbon-carbon double bond. |
| Alkyne | A hydrocarbon with at least one carbon-carbon triple bond. |
| Isomers | Compounds that share a molecular formula but have different structures or arrangements in space. |
| Functional group | A specific group of atoms on a carbon chain that gives the molecule its characteristic reactions and properties. |
| Polymer | A large molecule made of many repeating monomer units bonded together. |
| Triglyceride | A molecule made of one glycerol joined to three fatty acids through ester bonds, the main component of fats and oils. |
| Nucleophile | An electron-rich species that donates an electron pair to form a new bond. |
| Electrophile | An electron-poor species that accepts an electron pair to form a new bond. |
Both have a C=O, so they look alike at a glance. Check the position. An aldehyde's carbonyl is at the end of the chain with an H attached (-CHO, name ends in -al). A ketone's carbonyl sits between two carbons (name ends in -one).
Both contain an oxygen between carbon groups, so the names blur together. An ester has a C=O right next to that oxygen (-COO-), while an ether has only the single R-O-R' link. If you see a carbonyl beside the oxygen, it is an ester.
These are opposites, and the names do not obviously say which is which. Condensation builds a larger molecule and usually releases water. Hydrolysis splits a molecule by adding water, which you can remember because "hydro" means water and "lysis" means splitting.
Skeletal and condensed formulas hide hydrogens, so it is easy to undercount them. Every carbon needs exactly four bonds, so count each carbon's bonds to other atoms and fill the rest with H. Then check your answer against for an open-chain alkane or for an open-chain alkene with one double bond.