This is a great question to keep things in perspective....but it could save time with all u geniuses. THE POINT OF THIS THREAD IS THE FOLLOWING: WE MAY GET QUESTIONS ON WHAT EFFECT DOES CHANGING THE MOLECULE HAVE ON ITS PHYSICAL PROPERTIES SO WHY NOT ACCOUNT FOR ALL OF THEM RIGHT HERE ON SDN!! Some are more obvious then others, some are slightly stated in the book....but lets get the facts straight. Lets ignore functional groups for now. So say you have a starting compound with pentane. What effect does doing the following have an effect on Boiling point, melting point, heat of hydrogenation, heat of combustion, COMPARED to Pentane if you change pentane. 1.) Example: Extend length by -Ch3 group (i,e,- hexane)- it would increase BP and Increase MP, but even more because more nonpolar group, heat of combustion and hydrogenation probably increases with another carbon methyl group. 2.) Branching, i.e. - 2-methylbutane- compared to pentane, both have 5 carbons, but branching would increase MP because now it is more easily packed, and decrease BP because more condensed, not sure about solubility, but I assume Heat of hydorgenation and combustion are less because molecule is more compact. etc.... do you catch my where im going..so what would UNSATURATION, i.e.- pentene do on those factors.. Now if we account for adding functional groups....does the order of acidity chart parallel that of higher BP, higher MP, higher heat of hydr and comb....for example..does the acidity chart ORDER of compounds if you know what i mean (carboxylic acids are most acidi followed by diketone compounds, followed by water, then alcohols, then acid chloride, then aldehyde, then ketone, then anhydride, then ester, then amide, then prob like ethers, etcc...weak bases) so is the MOST acidic also the one with hte highest mp, bp, heat of hydr, comb.... Other properties (chemical) like bond energy and bond length are probably more obvious with the hybridization ideas.