Comprehensive Study Guide to Hydrocarbons: Structure, Properties, and IUPAC Nomenclature

Structure and Representation of Organic Molecules

• Overview of Structural Drawing Methods:
  • Organic molecules are frequently large and complex. Shorthand drawing techniques allow chemists to represent molecules conveniently without depicting every individual atom and bond.
  • Shorthand conventions clarify bond angles, depict relative spatial positions, and remove extraneous hydrogen atoms that obscure the functional carbon backbone.
  • The primary representation conventions include Kekulé (straight-line) structures, condensed formulas, skeletal (bond-line or zig-zag) formulas, and dashed-wedged line structures.

• Kekulé (Straight-Line) Structures:

  • Resemble Lewis structures, but each two-electron covalent bond is depicted as a straight line or dash rather than a pair of dots.
  • Bond multiplicity is indicated by dash count: a single line represents a single covalent bond, two parallel lines denote a double bond, and three parallel lines represent a triple bond.
  • Nonbonding valence electrons (lone pairs) are either shown explicitly as pairs of electron dots on heteroatoms or omitted with the assumption that the octet is satisfied.

• Condensed Structural Formulas:

  • Composed of elemental symbols showing the sequential order and connectivity of atoms within a single typographic line.
  • Atoms bonded to a central atom directly follow it (e.g., $CH_3$, $CH_2$, $NH$, $OH$).
  • Formulas can be interpreted from either direction; for instance, $H_3C-$ is chemically identical to $-CH_3$.
  • Branch points and functional groups are frequently enclosed in parentheses, such as $ClCH_2CH_2CH(OCH_3)CH_3$.

• Bond-Line (Skeletal or Zig-Zag) Formulas:

  • Carbon atoms are represented by line vertices (intersections) and line termini; the letter "C" is omitted.
  • Hydrogen atoms bonded directly to carbon are omitted from the drawing; each carbon atom is assumed to possess sufficient hydrogen atoms to complete its tetravalent octet (four total covalent bonds).
  • Heteroatoms (all atoms other than carbon and hydrogen, such as $O$, $N$, $S$, halogens) are explicitly written out.
  • Hydrogen atoms attached directly to heteroatoms (such as $-OH$ or $-NH_2$) must always be drawn.
  • Lone-pair electrons on heteroatoms are typically omitted but assumed present to satisfy octet requirements.

• Dashed-Wedged Line Structures (Three-Dimensional Representations):
  • Three-dimensional spatial arrangements are essential because stereoisomers can have identical connectivity and molecular formulas while representing distinct chemical substances.
  • Solid straight line: Represents a bond lying in the plane of the page or paper.
  • Solid wedge: Represents a bond pointing forward out of the plane of the paper, toward the viewer (in front).
  • Dashed wedge/line: Represents a bond directed backward, away from the viewer, behind the plane of the paper (behind).

• Structural Representation Worked Exercises:
  • Determining Hidden Hydrogens and Carbons:
  • In skeletal drawing representations of polyenes or cyclic systems (e.g., retinol, $C_{20}H_{30}O$), every vertex in the cyclohexenyl ring and polyene side chain represents a carbon atom. Hydrogens are deduced by calculating $4 - (\text{number of visible bonds})$.
  • For oxygen atoms in neutral ethers or alcohols ($-O-$ or $-OH$), two unshared electron pairs (four nonbonding electrons) are present to complete the octet.
  • Molecular Formula Determinations:
  • A bicyclic system comprising a benzene ring fused to a 4-membered azetidine ring bearing a $-NH-$ group and a $CH_2$ vertex has the molecular formula $C_7H_7N$.
  • 1-Pentene ($CH_2=CH-CH_2-CH_2-CH_3$) has the molecular formula $C_5H_{10}$.
  • Cyclopentadienone has the molecular formula $C_5H_4O$.
  • 3,5-Dibromocyclopentene has the molecular formula $C_5H_6Br_2$.

Classification of Hydrocarbons

• Definition of Hydrocarbons:

  • Hydrocarbons are binary organic compounds containing exclusively carbon and hydrogen atoms.

• Aliphatic Hydrocarbons:

  • Hydrocarbons that do not contain an aromatic ring system. Subdivided into:
  • Alkanes: Hydrocarbons containing solely single covalent bonds between carbon atoms (e.g., ethane, $C_2H_6$).
  • Alkenes: Hydrocarbons possessing one or more carbon-carbon double bonds ($C=C$) (e.g., ethylene/ethene, $C_2H_4$).
  • Alkynes: Hydrocarbons possessing one or more carbon-carbon triple bonds ($C \equiv C$) (e.g., acetylene/ethyne, $C_2H_2$).

• Aromatic Hydrocarbons (Arenes):

  • Hydrocarbons characterized by cyclic, planar, conjugated pi-electron systems exhibiting distinct aromatic stability and chemical behavior substantially different from aliphatic hydrocarbons.
  • The archetypal aromatic hydrocarbon is benzene ($C_6H_6$).

• Saturated vs. Unsaturated Hydrocarbons:

  • Saturated Hydrocarbons: Hydrocarbons containing exclusively single carbon-carbon bonds, bonding the maximum possible number of hydrogen atoms to the carbon framework. This class includes acyclic alkanes and cycloalkanes.
  • Unsaturated Hydrocarbons: Hydrocarbons possessing one or more multiple bonds (double bonds, triple bonds, or aromatic systems). Encompasses alkenes, alkynes, and arenes. Multiple bonds act as reactive functional regions for addition and substitution chemistry.

Alkanes and Cycloalkanes

• Acyclic Alkanes:

  • Saturated aliphatic hydrocarbons having the general molecular formula $C_n H_{2n+2}$, where $n = 1, 2, 3, \dots$
  • Composed exclusively of $sp^3$-hybridized carbon atoms forming tetrahedral geometries with bond angles of approximately $109.5^\circ$.

• Cycloalkanes:

  • Saturated hydrocarbons containing a closed ring of three or more carbon atoms.
  • Monocyclic cycloalkanes possess the general molecular formula $C_n H_{2n}$, reflecting the loss of two hydrogen atoms relative to acyclic alkanes due to ring closure.

• Continuous-Chain Alkanes (Homologous Series):

  • Methane: $CH_4$ (IUPAC prefix meth-)
  • Ethane: $C_2H_6$; $CH_3-CH_3$ (IUPAC prefix eth-)
  • Propane: $C_3H_8$; $CH_3-CH_2-CH_3$ (IUPAC prefix prop-)
  • Butane: $C_4H_{10}$; $CH_3-CH_2-CH_2-CH_3$ (IUPAC prefix but-)
  • Pentane: $C_5H_{12}$; $CH_3-(CH_2)_3-CH_3$ (IUPAC prefix pent-)
  • Hexane: $C_6H_{14}$; $CH_3-(CH_2)_4-CH_3$ (IUPAC prefix hex-)
  • Heptane: $C_7H_{16}$; $CH_3-(CH_2)_5-CH_3$ (IUPAC prefix hept-)
  • Octane: $C_8H_{18}$; $CH_3-(CH_2)_6-CH_3$ (IUPAC prefix oct-)
  • Nonane: $C_9H_{20}$; $CH_3-(CH_2)_7-CH_3$ (IUPAC prefix non-)
  • Decane: $C_{10}H_{22}$; $CH_3-(CH_2)_8-CH_3$ (IUPAC prefix dec-)

• Alkyl Groups:

  • Substituents formed by the hypothetical removal of a hydrogen atom from an alkane, denoted by the suffix -yl.
  • Continuous-chain alkyl groups: methyl ($-CH_3$), ethyl ($-CH_2CH_3$), propyl ($-CH_2CH_2CH_3$), butyl ($-CH_2(CH_2)_2CH_3$), pentyl ($-CH_2(CH_2)_3CH_3$), hexyl ($-CH_2(CH_2)_4CH_3$).
  • Branched alkyl groups:
  • Isopropyl (1-methylethyl): $-CH(CH_3)_2$
  • sec-Butyl (1-methylpropyl): $-CH(CH_3)CH_2CH_3$
  • Isobutyl (2-methylpropyl): $-CH_2CH(CH_3)_2$
  • tert-Butyl (1,1-dimethylethyl): $-C(CH_3)_3$

• IUPAC Nomenclature for Acyclic Alkanes:
  • Rule 1 (Parent Chain): Identify the longest continuous chain of carbon atoms. This chain determines the parent alkane name.
  • Rule 2 (Numbering): Number the carbon atoms of the parent chain starting from the terminal carbon nearest to a substituent group. This assigns the first substituent the lowest possible numerical locant.
  • Rule 3 (Single Substituent): Locate and designate the substituent by its locant number, separated by a hyphen from the substituent name, prefixed to the parent name (e.g., 2-methylpentane).
  • Rule 4 (Identical Substituents): When two or more identical substituents are present, indicate the multiplicity using Greek prefixes (di-, tri-, tetra-, penta-, etc.). Assign each substituent a specific location number; separate multiple numbers with commas (e.g., 2,4-dimethylpentane, 3,3-dimethylpentane).
  • Rule 5 (Different Substituents and Alphabetization):
  • List different alkyl groups in alphabetical order preceding the parent chain name.
  • Numerical multiplier prefixes (di-, tri-, tetra-) are ignored during alphabetization (e.g., dimethyl is alphabetized under "m").
  • Hyphenated structural prefixes sec- and tert- are ignored (e.g., sec-butyl and tert-butyl are alphabetized under "b").
  • Non-hyphenated prefixes such as iso- and cyclo- are considered part of the alkyl name and are alphabetized (e.g., isopropyl is alphabetized under "i"; cyclopropyl under "c").
  • Rule 6 (IUPAC Punctuation):
  • Commas separate adjacent numbers ($2,3$).
  • Hyphens separate numbers from letters ($2\text{-methyl}$, 4\text{-ethyl}$).\n * No hyphens, commas, or spaces are placed between the final substituent and the parent alkane name (e.g., 4-ethyl-2,3-dimethyl-5-propylnonane).\n\n\n\n* **IUPAC Nomenclature for Cycloalkanes**:\n * The ring serves as the root base name prefixed with *cyclo-*.\n * *Rule 1 (Monosubstituted Rings)*: If only one substituent is attached to the ring, no numerical locant is necessary (e.g., ethylcyclopentane).\n * *Rule 2 (Disubstituted Rings)*: Assign carbon-1 to the substituent having higher alphabetical priority, and number around the ring in the direction (clockwise or counterclockwise) that gives the second substituent the lowest possible locant.\n * *Rule 3 (Polysubstituted Rings)*: When three or more substituents are present, number the ring carbons to achieve the lowest overall set of locants at the first point of difference. If two different numbering sequences yield identical sets of locants, number in alphabetical priority order.\n * Example: 3-Ethyl-1,1-dimethylcyclohexane (correct substitution pattern is 1,1,3$, which takes precedence over$1,3,3 regardless of alphabetization at carbon-1).\n * *Rule 4 (Rings as Substituents)*: If a cycloalkane ring contains fewer carbon atoms than the acyclic chain to which it is bonded, the compound is named as an alkane with a cycloalkyl substituent (e.g., 3-cyclobutylpentane).\n\n* **Complex Substituent Nomenclature**:\n * When an alkyl substituent contains intricate branching not adequately named by common terms, systematic naming is applied.\n * Numbering of the complex substituent chain strictly begins at carbon-1 (C1) at the direct point of attachment to the parent chain.\n * Identify the longest continuous chain extending from C1, name its branches, and append the suffix *-yl*.\n * Multiplicity of identical complex substituents is indicated using multiplicative prefixes: *bis-* (2), *tris-* (3), *tetrakis-* (4), *pentakis-* (5), instead of *di-*, *tri-*, etc.\n * When comparing identical complex substituent terms, the lowest locant at the first cited point of difference within the complex substituent is listed first.\n\n* **Isomerism in Alkanes**:\n * *Constitutional (Structural) Isomers*: Compounds having identical molecular formulas but differing in the connectivity of their atoms.\n * Butane (C_4H_{10}) has 2 constitutional isomers: unbranched butane and 2-methylpropane (isobutane).\n * Pentane (C_5H_{12}) has 3 constitutional isomers: pentane, 2-methylbutane (isopentane), and 2,2-dimethylpropane (neopentane).\n * *Conformational Isomers (Conformers)*: Stereoisomers that have the same molecular formula and atom connectivity but differ in their three-dimensional spatial arrangements resulting from free rotation about carbon-carbon single (\sigma) bonds.\n\n\n\n\n\n\n\n* **Physical Properties of Alkanes and Cycloalkanes**:\n * *Solubility*: Nonpolar molecules; insoluble (immiscible) in polar solvents such as water, but readily soluble in nonpolar organic solvents.\n * *Density*: Lower than water (< 1.0\,g/cm^3); alkanes float on water.\n * *Boiling Points*:\n * Increase continuously with increasing carbon chain length or ring size due to cumulative London dispersion forces.\n * For unbranched alkanes at 1\,atm$: methane to butane ($C_1-C_4$) are gases; pentane to heptadecane ($C_5-C_{17}$) are liquids; higher alkanes ($C_{18}+) are solids.\n * Branching decreases the boiling point: a branched alkane has a lower surface area than an unbranched isomer, reducing intermolecular contact (e.g., 2-methyl-branched alkanes boil lower than unbranched isomers).\n * Cycloalkanes possess higher boiling points than their acyclic unbranched counterparts because ring rigidity allows closer intermolecular packing.\n\n\n\n* **Halogenated Alkanes (Alkyl Halides)**:\n * Hydrocarbon derivatives wherein one or more hydrogen atoms are substituted with halogens (F$,$Cl$,$Br$,$I).\n * *IUPAC Rules*:\n * Halogens are treated as substituents named *fluoro-*, *chloro-*, *bromo-*, and *iodo-*.\n * Halogens and alkyl groups possess equal rank in determining chain numbering; number from the chain terminus closest to any substituent.\n * If equidistant from both ends, assign the lower number based on alphabetical priority.\n * All substituents are listed alphabetically in the final name.\n * *Common Nomenclature*:\n * Named as alkyl halides: state the name of the alkyl group followed by the halide as a separate word (e.g., CH_3CH_2Cl$is chloroethane in IUPAC, ethyl chloride in common naming;$CH_3CH(Cl)CH_3 is 2-chloropropane in IUPAC, isopropyl chloride in common naming).\n * *Physical Properties of Halogenated Alkanes*:\n * Elevated boiling points relative to parent alkanes due to carbon-halogen bond polarity and resultant dipole-dipole interactions.\n * Densities: Unlike pure hydrocarbons, polyhalogenated alkanes (chloroalkanes containing two or more chlorine atoms, as well as bromoalkanes and iodoalkanes) have densities greater than water (> 1.0\,g/cm^3).\n\n# Alkenes and Cycloalkenes\n\n* **Definition and Structure of Alkenes**:\n * Acyclic unsaturated hydrocarbons containing at least one carbon-carbon double bond (C=C).\n * Functional group: C=C$double bond, comprising one strong$\sigma$bond (formed by$sp^2-sp^2$orbital overlap) and one weaker$\pi$bond (formed by sideways overlap of unhybridized$p orbitals).\n * Trigonal planar geometry exists around each double-bonded carbon with bond angles of approximately 120^\circ.\n * Monounsaturated acyclic alkenes have the general molecular formula C_n H_{2n}.\n * Historically called *olefins* ("oil-forming") due to the oily appearance of alkene dihalide addition products.\n * Simplest alkenes: ethene (C_2H_4$,$CH_2=CH_2$) and propene ($C_3H_6$,$CH_2=CH-CH_3).\n\n* **Cycloalkenes**:\n * Cyclic unsaturated hydrocarbons containing a C=C bond within the ring framework.\n * Monocyclic cycloalkenes possess the general molecular formula C_n H_{2n-2}, losing four hydrogens relative to acyclic alkanes (two from the ring, two from the double bond).\n * Simplest cycloalkene: cyclopropene (C_3H_4).\n\n* **IUPAC Nomenclature for Alkenes**:\n * *Rule 1 (Parent Chain)*: Identify the longest continuous carbon chain containing both carbon atoms of the double bond. Replace the alkane suffix *-ane* with *-ene*.\n * *Rule 2 (Chain Numbering)*: Number the chain starting from the terminal carbon closest to the double bond, ensuring the double bond receives the lowest possible locants. If the double bond is equidistant from both ends, number toward the first substituent branch point.\n * *Rule 3 (Locating the Double Bond)*: Designate the position of the double bond using the lower numerical locant of the two doubly bonded carbons, placing this number immediately prior to the parent alkene name or before the suffix (e.g., 2-hexene or hex-2-ene).\n * *Rule 4 (Polyenes)*: If two or more double bonds are present, use multiplying suffixes: *-diene*, *-triene*, *-tetraene*, preceded by all double bond locants (e.g., 1,4-pentadiene, 2-methyl-1,3,5-hexatriene).\n * *Rule 5 (Cycloalkenes)*: In cycloalkenes, the double-bonded carbons are automatically designated C1$and$C2. Number around the ring through the double bond in the direction that assigns substituents the lowest possible locants.\n\n* **Alkenyl Groups as Substituents**:\n * Noncyclic unsaturated substituents containing a double bond:\n * Methylene (common) / Methylidene (IUPAC): =CH_2$(bonded via double bond) or$-CH_2- attached to ring\n * Vinyl (common) / Ethenyl (IUPAC): -CH=CH_2\n * Allyl (common) / 2-Propenyl (IUPAC): -CH_2-CH=CH_2\n\n* **Geometric (Cis-Trans) Isomerism in Alkenes**:\n * Arises because the carbon-carbon double bond has restricted rotation at ambient temperatures due to the energy barrier of breaking the \pi$bond ($\sim 264\,kJ/mol).\n * *Prerequisite*: Each carbon of the double bond must be bonded to two non-identical groups. If either carbon possesses two identical groups, cis-trans isomerism is impossible.\n * *cis-Isomer*: The two similar or identical groups reside on the same side of the double bond plane.\n * *trans-Isomer*: The two similar or identical groups reside on opposite sides of the double bond plane.\n * Physical properties differ significantly between geometric isomers:\n * *cis*-2-Butene: Boiling point = 4^\circ C$, Density =$0.62\,g/mL\n * *trans*-2-Butene: Boiling point = 1^\circ C$, Density =$0.60\,g/mL\n * Multiple double bonds yield 2^n$possible geometric isomers (where$n is the number of stereogenic double bonds); 2,4-heptadiene has four distinct isomers: *trans-trans*, *trans-cis*, *cis-trans*, and *cis-cis*.\n\n\n\n* **Cahn-Ingold-Prelog (CIP) E-Z System**:\n * Standard stereochemical nomenclature system designed for tri- and tetra-substituted alkenes where *cis-trans* terminology becomes ambiguous.\n * *Rule 1 (Atomic Number Priority)*: Higher atomic number takes precedence over lower atomic number at each alkene carbon. Hydrogen (Z = 1) is the lowest possible priority.\n\n\n\n* *Rule 2 (Z vs. E Designation)*:\n * **(Z)** (*zusammen*, German for "together"): The higher-priority group on each carbon lies on the same side of the double bond.\n * **(E)** (*entgegen*, German for "opposite"): The higher-priority group on each carbon lies on opposite sides across the double bond.\n\n\n\n * *Rule 3 (Ties at Attached Atoms)*: If the atoms directly attached to the double bond carbon are identical, sequentially evaluate the atoms bonded to them in decreasing order of atomic number. Precedence is established at the first point of difference.\n * *Rule 4 (Outward Atom-by-Atom Comparison)*: Work outward step-by-step from the point of attachment. Compare atoms one by one, never summing group masses.\n * *Rule 5 (Multiple Bonds)*: Multiply-bonded atoms are treated as equivalent numbers of duplicate single bonds to that same atom:\n * Carbonyl group (-CH=O$) is treated as a carbon bonded to$(O, O, H).\n * Carboxylic acid/ester group (-CO_2R$) is treated as carbon bonded to$(O, O, O).\n * Alkenyl group (-CH=CH_2$) is treated as carbon bonded to$(C, C, H).\n * Alkynyl group (-C \equiv CH$) is treated as carbon bonded to$(C, C, C).\n\n* **Physical Properties of Alkenes**:\n * *Physical State at Room Temperature*:\n * C_2 - C_4: Gases\n * C_5 - C_{14}: Liquids\n * C_{15}+: Solids\n * *Solubility and Density*: Nonpolar, immiscible with water, less dense than water, soluble in organic solvents.\n * *Melting and Boiling Points*:\n * Boiling point increases with increasing carbon count and molecular weight.\n * Linear (unbranched) alkenes exhibit higher boiling points than branched isomers due to greater surface area.\n * *cis*-Alkenes typically have lower melting points than *trans*-alkenes due to packing inefficiencies caused by the bent molecular shape.\n * *Chemical Reactivity*: Substantially more reactive than alkanes; undergo addition reactions (halogenation, hydrogenation, hydrohalogenation, hydration), combustion, and polymerization.\n\n# Alkynes\n\n* **Structure and General Properties of Alkynes**:\n * Unsaturated acyclic hydrocarbons containing at least one carbon-carbon triple bond (C \equiv C).\n * The triple bond consists of one \sigma$bond (formed by$sp-sp$overlap) and two orthogonal$\pi$bonds (formed by overlap of unhybridized$2p_y$and$2p_z orbitals).\n * Linear geometry is present around the triple-bonded carbons with bond angles of 180^\circ.\n * Monounsaturated acyclic alkynes have the general molecular formula C_n H_{2n-2}.\n * Simplest alkyne: ethyne (C_2H_2, acetylene).\n\n* **IUPAC Nomenclature for Alkynes**:\n * Derived identically to alkene nomenclature, utilizing the suffix *-yne* instead of *-ene*.\n * The longest continuous carbon chain must contain the triple bond and is numbered from the end closer to the triple bond (e.g., 1-hexyne, 4-methyl-2-pentyne, 6,6-dimethyl-3-heptyne).\n * Multiple triple bonds use suffixes such as *-diyne*, *-triyne* (e.g., 1,6-heptadiyne).\n * Common names use "acetylene" as the parent: methylacetylene (CH_3-C \equiv CH$), dimethylacetylene ($CH_3-C \equiv C-CH_3).\n\n* **Nomenclature of Hydrocarbons with Double and Triple Bonds (Enynes)**:\n * When both a double and a triple bond exist in the same molecule, the compound is named as an **enyne**.\n * Suffix ordering: the suffix **-ene** always precedes **-yne** alphabetically in the final compound name (e.g., *-en-yne*).\n * *Numbering Priority*:\n * Number the continuous chain from the end closer to a multiple bond (whether double or triple) to assign the lowest possible locant set.\n * *Tiebreaker Rule*: If a double bond and a triple bond are equidistant from opposite ends of the chain, the **double bond takes precedence and receives the lower number**.\n * Example: CH_2=CH-CH_2-C \equiv CH is pent-1-en-4-yne (not pent-4-en-1-yne).\n * Example: HC \equiv C-CH=CH-CH_3$is pent-3-en-1-yne (triple bond at$C1$beats double bond at$C2 by first point of difference).\n\n\n\n* **Physical Properties of Alkynes**:\n * *Physical State at Room Temperature*:\n * C_2 - C_4: Gases\n * C_5 - C_{12}: Liquids\n * C_{13}+: Solids\n * Insoluble in water, soluble in nonpolar organic solvents, and less dense than water.\n * Boiling points increase incrementally with increasing carbon chain length.\n\n# Comprehensive Practice Exercises and Systematic Solutions\n\n* **Nomenclature and Structural Formulation of Alkanes and Cycloalkanes**:\n * *Compound 1*: CH_3CH_2CH(CH_3)C(CH_3)_2CH(CH_3)CH_2CH_2CH_3\n * Parent chain: Octane (8 carbons).\n * Numbering from left gives substituent locants at 3, 4, 4, 5 (lower than right-to-left 4, 5, 5, 6).\n * Substituents: 3,4,4,5-tetramethyl.\n * Systematic IUPAC Name: **3,4,4,5-Tetramethyloctane**.\n * *Compound 2*: Cyclohexane ring bearing an ethyl group and two methyl groups at positions yielding lowest locants:\n * Numbering starts at the carbon giving 1,2,4 substitution.\n * Systematic IUPAC Name: **1-Ethyl-2,4-dimethylcyclohexane**.\n * *Compound 3*: 2,2-Dimethyl-4-propylcyclohexane\n * Cyclohexane parent ring with two methyl groups on C2$and a propyl group ($-CH_2CH_2CH_3$) on$C4.\n * *Compound 4*: 3-Isopropyl-2,5-dimethylhexane\n * Hexane parent chain; methyl groups at C2$and$C5$; an isopropyl group ($-CH(CH_3)_2$) at$C3.\n * *Compound 5*: 3-Cyclopropyl-1,1-dimethylcyclopentane\n * Cyclopentane parent ring; two methyl groups at C1$; a cyclopropyl group ($-C_3H_5$) at$C3.\n\n* **Nomenclature of Halogenated Alkanes**:\n * CH_3-I: Iodomethane (Common: Methyl iodide)\n * CH_3-CH_2-CH_2-Cl: 1-Chloropropane (Common: Propyl chloride)\n * CH_3-CH(F)-CH_2-CH_3: 2-Fluorobutane (Common: *sec*-Butyl fluoride)\n * Chlorocyclobutane (Common: Cyclobutyl chloride)\n * CH_3-CH_2-CH_2-CH_2-Br: 1-Bromobutane (Common: Butyl bromide)\n * CH_3-CH(Cl)-CH_3: 2-Chloropropane (Common: Isopropyl chloride)\n * (CH_3)_3C-Cl: 2-Chloro-2-methylpropane (Common: *tert*-Butyl chloride)\n * Bromocyclohexane (Common: Cyclohexyl bromide)\n\n* **Nomenclature of Alkenes and Geometric Isomers**:\n * CH_3-CH=CH-CH_2-CH_2-CH_3: **2-Hexene** (or hex-2-ene)\n * CH_2=C(CH_2CH_3)CH_2CH_3: **2-Ethyl-1-butene**\n * CH_2=CH-CH(CH_3)_2: **3-Methyl-1-butene**\n * CH_2=C(CH_3)-CH=CH-CH=CH_2: **2-Methyl-1,3,5-hexatriene**\n * CH_2=C(CH_2CH_3)CH_2CH_2CH_3: **2-Ethyl-1-pentene**\n * 3,4-Dimethylcyclobutene: Four-membered ring with double bond at C1-C2$and methyl groups at$C3, C4.\n * 1-Ethylcyclopentene: Five-membered ring with double bond at C1-C2$and ethyl group at$C1.\n * 3,6-Dimethyl-1,4-cyclohexadiene: Six-membered ring with double bonds at C1$and$C4$, and methyl groups at$C3$and$C6.\n * 3-Ethyl-4-methyl-2-pentene: Condensed formula: CH_3-CH=C(CH_2CH_3)-CH(CH_3)-CH_3.\n * 2,3,4-Trimethyl-1-hexene: Condensed formula: CH_2=C(CH_3)-CH(CH_3)-CH(CH_3)-CH_2-CH_3.\n\n* **Cis-Trans Feasibility Determination**:\n * *1-Bromo-1-chloroethene* (BrClC=CH_2): Carbon-2 bears two identical hydrogen atoms; **no cis-trans isomers possible**.\n * *2-Chloro-2-butene* (CH_3-CCl=CH-CH_3$): Carbon-2 has$-Cl$and$-CH_3$; Carbon-3 has$-H$and$-CH_3. Both carbons have two different groups; **cis-trans (E-Z) isomers exist**.\n * *3-Chloropropene* (CH_2=CH-CH_2Cl): Carbon-1 bears two identical hydrogen atoms; **no cis-trans isomers possible**.\n * *3-Hexene* (CH_3CH_2-CH=CH-CH_2CH_3$): Both carbons have$-H$and$-CH_2CH_3; **cis-trans isomers exist**.\n * *4-Methyl-2-pentene* (CH_3-CH=CH-CH(CH_3)_2$): Carbon-2 has$-H$and$-CH_3$; Carbon-3 has$-H$and$-CH(CH_3)_2; **cis-trans isomers exist**.\n\n* **Nomenclature of Alkynes and Enynes**:\n * CH_3-CH_2-CH_2-CH_2-C \equiv CH: **1-Hexyne**\n * CH_3-C \equiv C-CH(CH_3)_2: **4-Methyl-2-pentyne**\n * CH_3-C(CH_3)_2-C \equiv C-CH_2-CH_2-CH_3: **2,2-Dimethyl-3-heptyne**\n * 6-Bromo-2-methylhex-2-en-4-yne: Chain numbered from right-to-left due to proximity of multiple bonds, with alkene prioritized in numbering ties.\n * 6,6-Dimethylhept-3-yne: A seven-carbon alkyne with a triple bond starting at C3$and two methyl branches at$C6.\n * 3,5-Dimethylhex-3-en-1-yne: Six-carbon enyne with alkyne at C1$and alkene at$C3$$.