Chemistry

12416 Hydrocarbonsn-pentaneisopentaneb.pt. = 36.1 o CDHf = -147 kJ/mol(-35.1 kcal/mol)DHc = - 3509 kJ/mol(- 839 kcal/mol)b.pt. = 30 o CDHf = -154.1 kJ/mol(-36.8 kcal/mol)DHc = -3502 kJ/mol(-837 kcal/mol)neopentaneb.pt. = 9.5 o CDHf = -168.0 kJ/mol(-40.1 kcal/mol)DHc = -3493 kJ/mol(- 835 kcal/mol)16.2.4. Relative StabilityBranched alkanes are more stable than linear alkanes, e.g. 2-methylpropane is morestable than n-butane.16.2.5 ReactivityThe Alkanes or Paraffins are inert towards acids, alkalies, oxidizing and reducing agentsunder normal conditions.Explanation:The unreactivity of Alkanes can be explained on the basis of inertness of a bond andnon-polar C-H/C-C bonds.(i)(ii)Inertness of bondIn a bond the electrons are very tightly held between the nuclei. A lot of energy is requiredto break it. Moreover, the electrons present in a bond can neither attack on anyelectrophile nor a nucleophile can attack on them. Hence Alkanes are less reactive.Non-polar Bonds:The electronegativity of carbon (2.5) and hydrogen (2.1) do not differ appreciably and thebonding electrons between C-H and C-C are equally shared making them almost nonpolar.In view of this, the ionic reagents such as acids, alkalies, oxidizing agents, etc find noreaction in the alkane molecules to which they could be attached.However, under suitable condition, Alkanes give two types of reactions.(i) Thermal and Catalytic Reactions(ii)Substituted Reactions.These reactions take place at high temperature or on absorption of light energy throughthe formation of highly reactive free radicals.