【正文】 1,4Dimethylcyclohexane trans1,4Dimethylcyclohexanethe diequatorialmethyl chair conformation is more stable by approximately 2 x () = kJ/mol cis1,4Dimethylcyclohexane The decalins Oxidation of AlkanesOxidation is the basis for their use as energy sources for heat and powerCombustion: a reaction with oxygen that takes place at high temperatures and converts alkanes to carbon dioxide and water.heat of bustion: heat released when one mole of a substance in its standard state is oxidized to carbon dioxide and water Heat of bustion for constitutional isomers For constitutional isomers [kJ (kcal)/mol] strain in cycloalkane rings as determined by heats of bustion Chlorination and Bromination of AlkanesAlkanes do react with chlorine or bromine to form alkyl chlorides or alkyl bromides. These halogenation reactions take place only at high temperatures or in the presence of light (symbolized by hv).Homolytic bond cleavage is the initiation step of the reaction because it creates the radical that is used in the first propagation stepA radical (often called a free radical) is a species containing an atom with an unpaired electron.propagation steps: the radical created in the first propagation step reacts in the second propagation step to produce a radical that can repeat the first propagation step.termination step: the step that helps bring the reaction to an end by decreasing the number of radicals available to propagate the reaction.radical substitution reaction: the reaction that radicals are involved as intermediates and the end result is the substitution of a halogen atom for one of the hydrogen atoms of the alkane.mechanism for the monobromination of ethaneFactors that Determine Product Distributionrelative stabilities of alkyl radicalsrelative rates of alkyl radical formation by a chlorine radical at room temperaturerelative rates of radical formation by a bromine radical at 125 176。 with respect to the other so that there is no overlap between 2p orbitals on adjacent carbonsCis,Trans Isomerism in AlkenesCis,trans isomers: isomers that have the same connectivity but a different arrangement of their atoms in space due to the presence of either a ring or a carboncarbon double bondIUPAC Nomenclature1. Number the longest chain of carbon atoms that contains the double bond in the direction that gives the carbons of the double bond the lowest numbers2. Locate the double bond by the number of its first carbon3. Name substituents4. Number the carbon, locate and name substituents, locate the double bond, and name the main chainCommon NamesDespite the precision and universal acceptance of IUPAC nomenclature, some alkenes, particularly lowmolecularweight ones, are known almost exclusively by their mon namesThe Cis,Trans SystemIf one of the sp2 carbons of the double bond is attached to two identical substituents, there is only one possible structure for the alkene. In other words, cis and trans isomers are not possible for an alkene that has identical substituents attached to one of the doublebonded carbons.uses priority rules if groups of higher priority are on the same side, the configuration is Z (German, zusammen)if groups of higher priority are on opposite sides, the configuration is E (German, entgegenthe two isomers are different pounds with different physical properties, such as different boiling points and different dipole moments.The relative priorities of the two groups bonded to an carbon are determined using the following rules:Rule 1. The relative priorities of the two groups depend on the atomic numbers of the atoms that are bonded directly to the carbon. The greater the atomic number, the higher is the priority.Rule 2. If the two substituents bonded to an sp2 carbon start with the same atom (there is a tie), you must move outward from the point of attachment and consider the atomic numbers of the atoms that are attached to the “tied” atoms.Rule 3. If an atom is doubly bonded to another atom, the priority system treats it as if it were singly bonded to two of those atoms. If an atom is triply bonded to another atom, the priority system treats it as if it were singly bonded to three of those atoms.Rule 4. In the case of isotopes (atoms with the same atomic number, but different mass numbers), the mass number is used to determine the relative priorities. Reaction Mechanism electrophile : An electrondeficient atom or molecule is called an electrophile. nucleophile : An electronrich atom or molecule is called a nucleophile. Reaction MechanismsA reaction mechanism describes how a reaction occurswhich bonds are broken and which new ones are formedthe order and relative rates of the various bondbreaking and bondforming stepsif in solution, the role of the solventif there is a catalyst, the role of a catalystthe position of all atoms and energy of the entire system during the reactionGibbs free energy change, ΔG0: a thermodynamic function relating enthalpy, entropy, and temperatureexergonic reaction: a reaction in which the Gibbs free energy of the products is lower than that of the reactants。 a reaction in which heat is absorbedEnergy diagram: a graph showing the changes in energy that occur during a chemical reactionReaction coordinate: a measure in the change in positions of atoms during a reactionActivation EnergyTransition state: an unstable species of maximum energy formed during the course of a reactiona maximum on an energy diagramActivation Energy, DG?: the difference in Gibbs free energy between reactants and a transition stateif DG? is large, few collisions occur with sufficient energy to reach the transiti