1 Chapter 2 AlkaneClassification of Hydrocarbon:hydrocarbonaliphaticaromaticsaturated: alkaneunsaturated: alkene, alkynealicyclic non-benzenoidbenzenoid2AlkanesHydrocarbons having no double or triple bond functional groups are classified as alkanes or cycloalkanes, depending on whether the carbon atoms of the molecule are arranged only in chains or also in rings. 3The alkanes and cycloalkanes are also members of a larger class of compounds referred to as aliphatic. Simply put, aliphatic compounds are compounds that do not incorporate any aromatic rings in their molecular structure.hydrocarbonaliphaticaromaticsaturated: alkane, cycloalkaneunsaturated: alkene, alkynealicyclic: cycloalkane, cycloalkene脂肪族脂肪族芳香族芳香族4Section 1 Molecular Structure of Alkane 5The simplest of the alkane is methane, CH4. . Chemical bone of alkaneplanar square tetrahedron6CH4 is a symmetrical molecule . Four C H bonds are equal.7sp3 hybrid orbital: A hybrid orbital made by the combination of one s orbital and three p orbitalsSp3 hybridground stateexcitation state基态激发态C electronic configuration in alkane89The carbon in methane is hybridized sp3 ( 25%s character, 75% p character ) and orbitals are directed toward the corner of a tetrahedron. 10The resulting H C H angles are 109.5(exactly, 10928) and the length of a carbon -hydrogen bond in methane is 1.09. 1.0911The four hydrogen atoms, each with an electron in a 1s orbital, overlap with the hybrids to form bonding ( orbital = sp3 + 1s ) which can rotate freely. 12.General formula Alkanes all have the molecular general formula CnH2n+2homologous series（同系列）（同系列）: The series compounds of the general formula and structural feature.Homolog（同系物）（同系物）: The compounds in homologous series. 13methane 甲甲 CH4 CH4 1 ethane 乙乙 C2H6 CH3CH3 1propane 丙丙 C3H8 CH3CH2CH3 1butane 丁丁 C4H10 CH3CH2CH2CH3 2pentane 戊戊 C5H12 CH3(CH2)3CH3 3hexane 己己 C6H14 CH3(CH2)4CH3 5heptane 庚庚 C7H16 CH3(CH2)5CH3 9octane 辛辛 C8H18 CH3(CH2)6CH3 18nonane 壬壬 C9H20 CH3(CH2)7CH3 35decane 癸癸 C10H22 CH3(CH2)8CH3 75NameMolecularFormulaStructuralFormulaIsomers141. The formulas and structures of these alkanes increase uniformally by a CH2 increment. 2. A uniform variation of this kind in a series of compounds is called homologous. 3. These formulas all fit the CnH2n+2 rule. This is also the highest possible H/C ratio for a stable hydrocarbon.4. Since the H/C ratio in these compounds is at a maximum, we call them saturated (with hydrogen). Summary:15. Types of carbon atom According to the links of carbon atoms, there are four types in carbon atoms. A primary carbon (1，伯伯) is attached to only one other carbon atom. Secondary carbon (2，仲仲) are attached to two carbons and tertiary carbons (3，叔叔) to three. A quaternary carbon(4，季季) atom is attached four other carbons.16 CH3 CH3 CH CH2 C CH2CH3 CH3 CH3primarycarbontertiarycarbonquaternarycarbonsecondarycarbon17Section 2 Nomenclature.Common namesmethane , ethane , propane , butane , pentane ,hexane , heptane , octane , nonane , decaneThe IUPAC（International Union of Pure and Applied Chemistry (IUPAC) 国际纯粹与应用化学联合会）assign the names to simple continuous-chain alkanes from C-1 to C-10. A common ane suffix identifies these compounds as alkanes.18Beginning with butane (C4H10), and becoming more numerous with larger alkanes, we note the existence of alkane isomers. n-butan，（正）丁烷i-butan，异丁烷iso, i，异19n-pentane, 正戊烷i-pentane, 异戊烷neo-pentane, 新戊烷C5H12 20there are five C6H14 isomers, shown below as abbreviated line formulas (A through E):21Although these distinct compounds all have the same molecular formula, only one (A) can be called hexane. How then are we to name the others?For the above isomers of hexane the IUPAC names are: B 2-methylpentane C 3-methylpentane D 2,2-dimethylbutane E 2,3-dimethylbutaneC6H14:22The IUPAC system（系统命名法）we have names for simple unbranched chains, as noted abovewe have names for simple unbranched chains, as noted abovethe ane suffix is replaced by yl in naming groups. The symbol R is used to designate a generic (unspecified) alkyl group 23alkyl groups:CH3 methylCH3CH2 ethyl CH3CH2CH2 propyl, CH3CH isoprpoyl CH3 CH3CH3(CH2)3 CH3CHCH2 CH3C CH3 CH3butyl isobutyl tert-butylR alkyl特特24Isomer are named using n-, iso-, and neo-. 1) The straight-chain alkane is named normal alkane (n-alkane, usually n- is omited). CH3CH2CH2CH2CH3 n-pentane25. IUPAC Rules for Alkane Nomenclature 2612345671234567272812345671234567293031D 2,2-dimethylbutane E 2,3-dimethylbutaneC6H14:32123456123453-methylhexane33123456712345673-ethyl-2-methylheptane343-chlorohexaneCl123456Cl123456Cl353-methylhexane12345623451561234362,3,6-trimethylheptane1234567123456737FF3,3-difluorohexane2-chloro-3-fluorobutaneClF1234not 3-chloro-2-fluorobutanenot 2-fluoro-3-chlorobutane384-bromo-3-methylhexane 4-tert-butyl-5-chlorooctane Br654321ClC(CH3)312345678not 3-bromo-4-methylhexanenot 3-methyl-4-bromohexanenot 4-chloro-5-tert-butyloctane3912345612345673-ethyl-2,2,5-trimethylhexane3,4-dichloro-4-ethyl-5-methylheptane40Section 3 Isomerism of Alkane. carbon-chain isomerIsomers: Molecules have the same formula but different structures.carbon-chain isomers: Molecules have the same formula but different structure of carbon-chains.41C4H10n-butaneiso-butane or 2-methylpropaneC5H10n-pentane neo-pentaneor 2,2-dimethylpropaneiso-pentaneor 2-methylbutane42.conformational isomer （构象异构）（构象异构）Conformation:The three-dimensional structure of a molecule. Conformational isomers are interconverted by rotations about bonds. 43Because rotations of bond C-C , countless conforma-tional isomer would be formed. The conformationsare expressed by sawhorse formula（锯架式）（锯架式） or Newman projection formula（纽曼投影式）（纽曼投影式）. HHHHHHHHHHHHsawhorse formulaNewman projection formula44ethane45Extreme Conformations of Ethane (CH3CH3)Name ofConformerWedge-HatchedBond StructureSawhorseStructureNewmanProjection重叠式构象交叉式构象46Potential Energy Profile for Ethane ConformersDihedral Angle47Butane Conformations (CH3CH2CH2CH3)48对位交叉式部分重叠式邻位交叉式全重叠式49Potential Energy Profile for Butane Conformers全重叠式全重叠式对位交叉式部分重叠式部分重叠式邻位交叉式邻位交叉式50conformation eclipsed staggeredmolecule energy high lowstability unsteadiest steadiestcompare two conformation: 51 Section 4 Properties of Alkane. Physical properties C1 C4 alkanes colorless gasesC5 C16 alkanes clear liquidsC17 alkanes white solids The boiling points increase as the number of carbonsin the molecule increases. Because the boiling point is a measure of the ease of breaking up intermolecularattractive forces which called van der Waals forces. 52. Chemical properties1) Stability The alkanes are so steady that can not react with strong acids, alkalies, oxidants, reducers.532) Halogenation(substitution)The halogenation of alkane is a free-radical chain reaction.CH4 CH3Cl CH2Cl2 CHCl3 CCl4Cl2h Cl2h Cl2h Cl2h ultraviolet radiation or high temp.54Reaction mechanism:chain-initiating:Cl2 Cl + ClCl + CH4 CH3 + HClchain-terminating:Cl + Cl Cl2CH3 + Cl CH3ClCH3 + CH3 CH3CH3chain-propagating:CH3 + Cl2 CH3Cl + ClCH3Cl + Cl CH2Cl + HClCH2Cl + Cl2 CH2Cl2 + Cl55Activity of halogen:F Cl Br I56 CH3CH3 C CH3CH3CHCH3CH3CH2CH3The radical is more steady, and more easy to be formed. Stability of radicals:bond dissociation energy(kJmol-1)CH3H CH3CH2H (CH3)2CHH (CH3)3CH 435 410 397 38557CH3CHCH3 CH3Cl2h CH3CHCH2Cl CH3 ClCH3 C CH3 CH3+ 1-chloro-2-methylpropane 2-chloro-2-methylpropane48%29%yield:58 Exercisepage 31. 2-4. (1) (2) (3) 2-6. 2-12.