Appendix A: Functional Group Atlas
This appendix collects the functional groups introduced in Chapter 1 into a single structured reference: identity, geometry, polarity, hybridization, and typical reactivity for each group, followed by a family tree and an interconversion map showing how groups transform into one another across the handbook.
How to Read an Entry
Each entry lists five things:
- Structure — the defining atoms and bonds, written in condensed form.
- Hybridization — the orbital hybridization of the key atom(s) in the group.
- Geometry — the approximate bond angle and shape around that atom.
- Polarity — whether the group is polar or nonpolar, and why.
- Typical reactivity — the kind of chemistry the group tends to undergo, in one or two sentences.
These five properties are the ones used repeatedly throughout the handbook to predict how an unfamiliar molecule will behave.
Hydrocarbons
Alkanes
Structure: C–C and C–H single bonds only (e.g., CH₃CH₂CH₃) Hybridization: sp³ at carbon Geometry: Tetrahedral, ~109.5° Polarity: Nonpolar Typical reactivity: Low. Undergo radical halogenation and combustion but do not react with most common reagents. Function as the unreactive “scaffold” that other functional groups attach to.
Alkenes
Structure: C=C double bond (e.g., CH₂=CH₂) Hybridization: sp² at both alkene carbons Geometry: Trigonal planar, ~120° Polarity: Weakly polar; the π bond is polarizable and electron-rich Typical reactivity: The π electrons act as a nucleophile. Undergoes electrophilic addition (Chapter 9) — addition of HX, H₂O, X₂, and hydrogenation all convert the double bond into two new single bonds.
Alkynes
Structure: C≡C triple bond (e.g., CH≡CH) Hybridization: sp at both alkyne carbons Geometry: Linear, 180° Polarity: Weakly polar Typical reactivity: Similar to alkenes but with two π bonds available; undergoes one or two successive additions (Chapter 9). Terminal alkyne C–H is unusually acidic (Chapter 3) due to the high s-character of the sp carbon.
Arenes (Aromatic Rings)
Structure: Six-membered ring of sp² carbons with a delocalized, cyclic π system (benzene, C₆H₆, is the parent) Hybridization: sp² at every ring carbon Geometry: Planar hexagon, 120° internal angles Polarity: Nonpolar overall, though substituents can introduce a dipole Typical reactivity: The delocalized π system resists addition (which would break aromaticity) and instead undergoes electrophilic aromatic substitution (Chapter 16), preserving the ring.
Halogen-Containing Groups
Alkyl Halides
Structure: C–X, where X = F, Cl, Br, or I Hybridization: sp³ at the carbon bearing the halogen Geometry: Tetrahedral, ~109.5° Polarity: Polar C–X bond (halogen is electronegative) Typical reactivity: The halogen is a good leaving group, so alkyl halides are the classic substrate for substitution (Chapter 7) and elimination (Chapter 8) reactions.
Oxygen-Containing Groups
Alcohols
Structure: C–O–H Hybridization: sp³ at carbon and at oxygen Geometry: Tetrahedral at carbon; bent (~108–109°) at oxygen Polarity: Polar; hydrogen bond donor and acceptor Typical reactivity: Weakly acidic at O–H (Chapter 3); the oxygen is nucleophilic, and the hydroxyl can be converted into a leaving group for substitution or eliminated to form an alkene (Chapter 8).
Phenols
Structure: Ar–O–H (hydroxyl attached directly to an aromatic ring) Hybridization: sp² at the ring carbon bearing oxygen; oxygen lone pair conjugates into the ring Geometry: Planar at the point of attachment Polarity: Polar; hydrogen bond donor and acceptor Typical reactivity: More acidic than alcohols (Chapter 3) because the conjugate base (phenoxide) is resonance-stabilized by the ring. The ring is also activated toward electrophilic aromatic substitution (Chapter 17).
Ethers
Structure: C–O–C Hybridization: sp³ at oxygen Geometry: Bent at oxygen, ~109.5° Polarity: Polar bonds, but no O–H means no hydrogen bond donation Typical reactivity: Relatively unreactive; commonly used as solvents rather than reactants. Lack a good leaving group under normal conditions.
Aldehydes
Structure: R–CHO (carbonyl carbon bonded to at least one hydrogen) Hybridization: sp² at the carbonyl carbon Geometry: Trigonal planar, ~120° Polarity: Strongly polar C=O dipole Typical reactivity: Carbonyl carbon is electrophilic and undergoes nucleophilic addition (Chapter 12). Less sterically hindered than ketones, so generally more reactive toward nucleophiles.
Ketones
Structure: R–CO–R′ (carbonyl carbon bonded to two carbon groups) Hybridization: sp² at the carbonyl carbon Geometry: Trigonal planar, ~120° Polarity: Strongly polar C=O dipole Typical reactivity: Undergoes nucleophilic addition (Chapter 12), generally somewhat slower than aldehydes due to greater steric bulk and electron donation from two alkyl groups.
Carboxylic Acids and Their Derivatives
These five groups share a carbonyl carbon attached to a heteroatom leaving group and undergo the same general reaction — nucleophilic acyl substitution (Chapter 13) — but differ enormously in reactivity depending on how good a leaving group that heteroatom provides.
Carboxylic Acids
Structure: R–COOH Hybridization: sp² at the carbonyl carbon Geometry: Trigonal planar, ~120° Polarity: Highly polar; O–H allows hydrogen bonding (carboxylic acids often exist as dimers) Typical reactivity: Acidic at O–H (Chapter 3); the conjugate base (carboxylate) is resonance-stabilized across both oxygens. Converted to acid chlorides, esters, and amides via nucleophilic acyl substitution.
Acid Chlorides
Structure: R–COCl Hybridization: sp² at the carbonyl carbon Geometry: Trigonal planar, ~120° Polarity: Very polar Typical reactivity: The most reactive carboxylic acid derivative — chloride is an excellent leaving group. Reacts readily with water, alcohols, and amines to generate acids, esters, and amides.
Anhydrides
Structure: R–CO–O–CO–R′ Hybridization: sp² at both carbonyl carbons Geometry: Trigonal planar at each carbonyl Polarity: Polar Typical reactivity: Second most reactive derivative, behind acid chlorides. A carboxylate is a moderate leaving group, so anhydrides readily acylate alcohols and amines.
Esters
Structure: R–CO–O–R′ Hybridization: sp² at the carbonyl carbon Geometry: Trigonal planar, ~120° Polarity: Polar Typical reactivity: Moderately reactive; undergoes hydrolysis back to the carboxylic acid or transesterification, but requires more forcing conditions than acid chlorides or anhydrides. Often recognizable by pleasant, fruity odors.
Amides
Structure: R–CO–NR′₂ Hybridization: sp² at the carbonyl carbon; nitrogen lone pair delocalizes into the carbonyl, making nitrogen effectively sp² as well Geometry: Planar across the whole C(=O)–N unit Polarity: Highly polar, but nitrogen’s lone pair is tied up in resonance Typical reactivity: The least reactive carboxylic acid derivative and the most stable — nitrogen is a poor leaving group because of resonance donation into the carbonyl. This same resonance makes amide nitrogen far less basic and less nucleophilic than amine nitrogen. Forms the peptide bond in proteins.
Acetals and Hemiacetals
Structure: Hemiacetal — a carbon bonded to one –OH and one –OR; Acetal — a carbon bonded to two –OR groups. Both form from addition of alcohol(s) to an aldehyde or ketone. Hybridization: sp³ at the central carbon (contrast with the sp² parent carbonyl) Geometry: Tetrahedral, ~109.5° Polarity: Polar C–O bonds Typical reactivity: Formed and hydrolyzed reversibly under acid catalysis (Chapter 12). Acetals are stable to base and are used as protecting groups to temporarily mask a carbonyl during a synthesis.
Nitrogen-Containing Groups
Amines
Structure: C–NR₂ (R = H or alkyl/aryl) Hybridization: sp³ at nitrogen (lone pair occupies the fourth position) Geometry: Trigonal pyramidal, ~107° Polarity: Polar; primary and secondary amines are hydrogen bond donors, and all amines are hydrogen bond acceptors Typical reactivity: The nitrogen lone pair is both basic (Chapter 3) and strongly nucleophilic — amines are common nucleophiles in substitution and acyl substitution reactions.
Amides
See Carboxylic Acids and Their Derivatives, above. Amides sit at the intersection of the oxygen- and nitrogen-containing families: the carbonyl places them among the acyl derivatives, while the nitrogen places them among biologically central nitrogen groups (proteins, peptides).
Aromatic Heterocycles
Structure: Aromatic rings containing one or more nitrogen, oxygen, or sulfur atoms in place of a ring carbon (e.g., pyridine, furan, pyrrole) Hybridization: sp² throughout the ring, maintaining the delocalized π system Geometry: Planar Polarity: Varies with the heteroatom; ring nitrogen lone pairs may or may not be part of the aromatic π system depending on whether they are conjugated into the ring Typical reactivity: Retains aromatic character and undergoes substitution rather than addition; the heteroatom strongly influences reactivity and where substitution occurs (Chapter 17). Widespread in pharmaceuticals and biomolecules.
Summary Table
| Functional Group | Structure | Hybridization | Geometry | Polarity | Typical Reactivity |
|---|---|---|---|---|---|
| Alkane | C–C, C–H | sp³ | Tetrahedral (109.5°) | Nonpolar | Unreactive scaffold |
| Alkene | C=C | sp² | Trigonal planar (120°) | Weakly polar | Electrophilic addition |
| Alkyne | C≡C | sp | Linear (180°) | Weakly polar | Addition; acidic terminal C–H |
| Arene | Delocalized ring | sp² | Planar hexagon | Nonpolar | Electrophilic aromatic substitution |
| Alkyl halide | C–X | sp³ | Tetrahedral | Polar | Substitution, elimination |
| Alcohol | C–O–H | sp³ | Tetrahedral / bent at O | Polar | Weak acid; nucleophile; substrate for substitution/elimination |
| Phenol | Ar–O–H | sp² | Planar | Polar | More acidic than alcohols; activates ring toward EAS |
| Ether | C–O–C | sp³ | Bent at O | Polar bonds, no H-bond donor | Largely unreactive; common solvent |
| Aldehyde | R–CHO | sp² | Trigonal planar | Strongly polar | Nucleophilic addition |
| Ketone | R–CO–R′ | sp² | Trigonal planar | Strongly polar | Nucleophilic addition |
| Carboxylic acid | R–COOH | sp² | Trigonal planar | Highly polar | Acidic; acyl substitution |
| Acid chloride | R–COCl | sp² | Trigonal planar | Very polar | Most reactive acyl substitution |
| Anhydride | R–CO–O–CO–R′ | sp² | Trigonal planar | Polar | Reactive acyl substitution |
| Ester | R–CO–O–R′ | sp² | Trigonal planar | Polar | Moderate acyl substitution; hydrolysis |
| Amide | R–CO–NR′₂ | sp² (C and N) | Planar | Polar, N lone pair delocalized | Least reactive acyl derivative; very stable |
| Acetal/Hemiacetal | C(OR)(OR)/C(OH)(OR) | sp³ | Tetrahedral | Polar | Reversible, acid-catalyzed; protecting group |
| Amine | C–NR₂ | sp³ | Trigonal pyramidal (~107°) | Polar | Basic; strongly nucleophilic |
| Aromatic heterocycle | Ring with N/O/S | sp² | Planar | Variable | Substitution; heteroatom-directed reactivity |
Functional Group Family Tree
- Hydrocarbons — carbon and hydrogen only
- Alkanes (single bonds)
- Alkenes (one or more C=C)
- Alkynes (one or more C≡C)
- Arenes (aromatic rings)
- Halogen-containing
- Alkyl halides
- Oxygen-containing
- Alcohols and phenols (C–OH)
- Ethers (C–O–C)
- Carbonyl-containing groups (C=O)
- Aldehydes and ketones (simple carbonyls — undergo addition)
- Carboxylic acid derivatives (carbonyl + heteroatom leaving group — undergo substitution)
- Carboxylic acids
- Acid chlorides
- Anhydrides
- Esters
- Amides
- Acetals and hemiacetals (carbonyl + alcohol addition products)
- Nitrogen-containing
- Amines
- Amides (also a carbonyl-containing group, above)
- Aromatic heterocycles — bridge the aromatic and heteroatom families
The single most useful split in this tree is between the simple carbonyls (aldehydes, ketones — no good leaving group, so they undergo addition) and the acyl derivatives (carboxylic acids and their relatives — a heteroatom leaving group is present, so they undergo substitution). This distinction, developed in Chapters 12 and 13, explains most of carbonyl chemistry.
Functional Group Interconversion Map
| Starting Group | Product | Typical Transformation | Chapter |
|---|---|---|---|
| Alkene | Alkyl halide | Electrophilic addition of HX or X₂ | 9 |
| Alkyl halide | Alkene | Elimination (E1/E2) | 8 |
| Alkyl halide | Alcohol | Substitution (SN1/SN2) with water or hydroxide | 7 |
| Alcohol | Alkyl halide | Substitution with SOCl₂, PBr₃, or acid + halide | 7 |
| Alcohol | Alkene | Acid-catalyzed dehydration (E1) | 8 |
| Alkene | Alcohol | Acid-catalyzed hydration (Markovnikov addition) | 9 |
| Alcohol | Aldehyde or ketone | Oxidation | 12 |
| Aldehyde or ketone | Alcohol | Reduction, or addition of a nucleophile | 12 |
| Aldehyde | Carboxylic acid | Oxidation | 12–13 |
| Aldehyde/ketone + alcohol | Hemiacetal, then acetal | Acid-catalyzed addition | 12 |
| Carboxylic acid | Acid chloride | Reaction with SOCl₂ | 13 |
| Acid chloride | Anhydride, ester, or amide | Nucleophilic acyl substitution | 13 |
| Ester | Carboxylic acid | Hydrolysis | 13 |
| Carboxylic acid + alcohol | Ester | Fischer esterification | 13 |
| Ester or acid chloride | Amide | Substitution with an amine | 13 |
| Ketone or aldehyde | Enol or enolate | Tautomerization, or deprotonation at the α-carbon | 14 |
| Benzene | Substituted arene | Electrophilic aromatic substitution (halogenation, nitration, sulfonation, Friedel-Crafts) | 16 |
Reading this table both directions is a useful exercise: given a target molecule, work backward through the map to identify which starting material and reaction would produce it — the core skill developed in retrosynthetic analysis (Chapter 21).
Cross-References
- Chapter 1 (Functional Groups) — first introduction to each group and its role in the handbook.
- Chapter 3 (Acids and Bases) — pKa trends referenced throughout this atlas; see also Appendix B (pKa Tables).
- Chapters 7–9 (Substitution, Elimination, Addition) — mechanisms behind the hydrocarbon and alkyl halide interconversions above.
- Chapters 12–14 (Carbonyl Chemistry) — mechanisms behind the carbonyl and acyl substitution interconversions above.
- Chapters 15–17 (Aromaticity) — mechanisms behind arene and heterocycle reactivity.
- Appendix C (Reaction Summary Tables) — condensed, exam-ready versions of the reactions referenced in the interconversion map.