HL IB Chemistry – Organic Functional Groups & Spectroscopic Analysis

Vocabulary flashcards summarising key terms from the lecture notes on organic compound representation, functional groups, nomenclature, isomerism, and analytical techniques (MS, IR, NMR).

Empirical Formula

Shows the simplest whole-number ratio of each type of atom in a compound.

Molecular Formula

Gives the actual number of each kind of atom present in a molecule.

Structural Formula

Displayed formula that shows every atom and every bond in a molecule.

Condensed Structural Formula

Compact written form that omits most single bonds while retaining enough detail to indicate connectivity.

Skeletal Formula

Line-angle diagram that represents carbon skeletons; carbon atoms appear at line ends/vertices and most H atoms are omitted.

Stereochemical Formula

3-D drawing using wedges/dashes to show the spatial arrangement of groups around a stereocentre.

Functional Group

Specific atom or group of atoms that gives an organic molecule its characteristic chemical properties.

Homologous Series

Family of compounds with the same functional group and general formula, differing by successive –CH₂– units.

Catenation

Ability of identical atoms (especially carbon) to form long chains by covalent bonding to themselves.

General Formula

Algebraic expression that represents the composition of every member of a homologous series (e.g. CₙH₂ₙ₊₂ for alkanes).

Alkane

Saturated hydrocarbon containing only single C–C bonds; suffix “-ane”.

Alkene

Unsaturated hydrocarbon containing at least one C=C double bond; suffix “-ene”.

Alkyne

Unsaturated hydrocarbon containing at least one C≡C triple bond; suffix “-yne”.

Halogenoalkane

Alkane derivative in which one or more H atoms are replaced by halogen atoms; prefixes fluoro-, chloro-, bromo-, iodo-.

Alcohol

Compound containing a hydroxyl (-OH) functional group attached to a saturated carbon; suffix “-ol”.

Aldehyde

Carbonyl compound with formula R-CHO where C=O is at the end of a chain; suffix “-al”.

Ketone

Carbonyl compound with formula R-CO-R′ where C=O is within a chain; suffix “-one”.

Carboxylic Acid

Compound containing the ‑COOH (carboxyl) group; suffix “-oic acid”.

Ether

Compound with an alkoxy (R-O-R′) linkage between two carbon groups.

Amine

Organic derivative of ammonia containing an amino (-NH₂, ‑NHR, or ‑NR₂) group; suffix “-amine”.

Amide

Compound containing a CONH₂, CONHR or CONR₂ group; suffix “-amide”.

Ester

Compound with the ‑COO- linkage formed from an acid and an alcohol; suffix “-oate” in IUPAC names.

Phenyl Group

Benzene ring treated as a substituent, represented as C₆H₅– or Ph-.

Aromatic Compound (Arene)

Molecule containing one or more delocalised π-electron ring systems (e.g. benzene).

Alkyl Group

Hydrocarbon substituent derived from an alkane by removing one H; ends in “-yl”.

IUPAC Nomenclature

Systematic set of rules for naming organic compounds established by the International Union of Pure and Applied Chemistry.

Side Chain

Carbon substituent attached to the main (longest) chain of a molecule.

Stem (Naming)

Part of an IUPAC name indicating the number of carbons in the parent chain (meth-, eth-, prop-, etc.).

Cis Isomer

Configurational isomer with two specified groups on the same side of a double bond or ring.

Trans Isomer

Configurational isomer with two specified groups on opposite sides of a double bond or ring.

Structural Isomerism

Compounds with the same molecular formula but different connectivity of atoms.

Functional Group Isomerism

Structural isomers that contain different functional groups.

Positional Isomerism

Structural isomers with the same functional group located at different positions on the carbon chain.

Branched-Chain Isomerism

Structural isomers differing by the arrangement of the carbon skeleton (branching).

Conformational Isomer

Isomer arising from rotation about a single σ-bond (e.g. staggered vs. eclipsed ethane).

Configurational Isomer

Isomer that can interconvert only by breaking bonds; includes cis-trans and optical isomers.

Newman Projection

Diagram showing the spatial orientation of substituents viewed along a particular C–C bond.

Chair Conformation

Most stable three-dimensional shape adopted by cyclohexane, minimising strain.

Boat Conformation

Less stable cyclohexane shape with eclipsed bonds and flagpole H repulsion.

Chiral Carbon (Chiral Centre)

Tetrahedral carbon atom bonded to four different atoms/groups, giving rise to optical activity.

Enantiomer

One of a pair of non-superimposable mirror-image molecules.

Diastereomer

Stereoisomers that are not mirror images; arise when a molecule has two or more chiral centres.

Optical Activity

Ability of a compound to rotate the plane of polarised light; shown by enantiomers.

Racemic Mixture

50:50 mixture of two enantiomers; overall optically inactive.

Molecular Ion Peak (M⁺)

Peak with the highest m/z in a mass spectrum, representing the unfragmented molecular cation.

M+1 Peak

Small mass-spectral peak one unit higher than M⁺, mainly due to the natural abundance of ¹³C.

Fragmentation Pattern

Set of peaks in a mass spectrum produced by the breakdown of the molecular ion into smaller ions.

Base Peak

Tallest peak in a mass spectrum; assigned 100% relative abundance.

Infrared (IR) Spectroscopy

Technique that identifies functional groups by measuring molecular vibrations that absorb IR radiation.

Wavenumber (cm⁻¹)

Unit equal to 1/λ; used on the x-axis of IR spectra to express absorption frequency.

Fingerprint Region

Complex IR region below about 1500 cm⁻¹ unique to each molecule; useful for identification by comparison.

Carbonyl Stretch

Strong IR absorption of C=O bonds typically near 1700 cm⁻¹.

Hydroxyl Stretch

Broad IR absorption of O–H bonds; ~3200–3600 cm⁻¹ for alcohols, broader 2500–3300 cm⁻¹ for acids.

Nuclear Magnetic Resonance (NMR)

Spectroscopy that detects the interaction of nuclear spins with an external magnetic field to reveal molecular structure.

Proton Environment

Set of chemically equivalent hydrogen nuclei experiencing the same electronic surroundings in a molecule.

Chemical Shift (δ)

Position of an NMR signal measured in ppm relative to TMS; indicates electronic environment.

Tetramethylsilane (TMS)

Reference compound (Si(CH₃)₄) that defines δ = 0 ppm in NMR spectra.

Integration Trace

Step-like line on an NMR spectrum whose step heights are proportional to peak areas and hence proton ratios.

Multiplicity

Splitting pattern of an NMR signal resulting from spin–spin coupling with neighbouring protons.

n+1 Rule

In proton NMR, a signal is split into (n + 1) peaks where n = number of adjacent protons.

Singlet

Unsplitted NMR signal indicating zero neighbouring protons.

Doublet

Two-line NMR splitting pattern produced by one neighbouring proton.

Triplet

Three-line NMR pattern produced by two equivalent neighbouring protons.

Quartet

Four-line NMR pattern produced by three equivalent neighbouring protons.

Shielding (NMR)

Electron density around a nucleus that reduces the effective magnetic field and shifts signals up-field (lower δ).

Deshielding

Reduction of electron density around a nucleus (e.g. near electronegative atoms), causing down-field shift (higher δ).

Mass-to-Charge Ratio (m/z)

Horizontal axis of a mass spectrum; mass of an ion divided by its charge.

London Dispersion Forces

Weak intermolecular forces arising from temporary dipoles; increase with molecular size and affect boiling points.

Functional Group Prefix

IUPAC syllable placed before the parent name to indicate a substituent (e.g. hydroxy-, bromo-).

Functional Group Suffix

IUPAC ending added to the parent name to indicate the principal functional group (e.g. ‑ol, ‑one).

Saturated Compound

Organic molecule containing only single bonds; holds maximum possible number of hydrogen atoms.

Unsaturated Compound

Organic molecule containing C=C, C≡C or aromatic rings; fewer hydrogens than the corresponding alkane.

Resonance (IR Context)

Condition when IR radiation matches a bond’s natural vibration frequency, leading to absorption.

Isotopic Abundance

Relative proportion of an isotope in a natural element; influences mass spectral peak heights.

Steric Hindrance

Spatial crowding of groups in a molecule that can inhibit reactions or influence conformations.

Hydrocarbon

Compound consisting solely of hydrogen and carbon atoms.

Free Rotation

Unrestricted twisting about a single σ-bond, allowing different conformations.

π-Bond

Sideways overlap of p-orbitals in double/triple bonds; restricts rotation.

σ-Bond

Single covalent bond formed by head-on orbital overlap along the internuclear axis.

Homologous Increment

Regular addition of a –CH₂– unit that causes gradual property changes within a homologous series.