Determination of boiling point of molecule?

Question

how to determine which molecule has highest boiling point eg:?given methyl ether and ethanol.what are the steps?i knw it depends on the type of bonding (to determine wether it has hydrogen bonding)but how do i knw? do i HAVE to draw the structure first?if dats is so,how to draw this complex molecule?i only know how to draw simple molecule like water,HCL,NaCL and other simple structure base on their lewis structure but i dont know how to draw complex molecule like ethanol,glucose and other molecule that has so many carbon...pls help me so dat i can sleep well tonite..

Answer 1

by DSC

Answer 2

To draw the structure of a molecule from the name you will either need some chemistry background (which might take several years) or you can look it up somewhere. One of the cheapest ways is to get an old copy of a chemical company catalog (such as Aldrich Chem Co). It gives the structure and basic properties bp, density, mp, refractive index, etc. and it's free. There are places on line where you can look up formulas also. Once you have the formula written out, look for places where hydrogen is directly attached to a small, electronegative element (oxygen, flourine, nitrogen). If this is the case, there will be hydrogen bonding and the boiling point will be quite a bit higher than, a molecule of similar molecular weight without it. If there is no hydrogen bonding and the molecule is not particularly polar, the bp will pretty much be proportional to molecular weight. Groups which introduce polarity will increase the boiling point by varying amounts.

I would suggest you look up bps for sets of related molecules and see how they relate to each other.  Try looking at the bps for the series of saturated hydrocarbons starting with ethane, then compare with the same list, but each having a double bond (ethylene etc) and then compare with the corresponding tripple bond compounds (acetylene) and so on. You can compare the hydrocarbons with the series of alcohols starting with methanol and with the corresponding series of aldehydes and organic acids (formaldehyde; formic acid). After a while you will get a feel for what factors affect the bp and by approximately what degree.

Answer 3

When you write "Methyl ether" you probably mean dimethyl ether: CH3-O-CH3;  the oxygen is in the middle and on either side are two methyl groups.  Ethanol is C2H5OH; draw two carbons with a single bond (line) between them.  On the left carbon, attach three Hydrogens (H) each H with a single line to the carbon; on the right carbon, attach two hydrogens, each with a single line to the carbon.  Then, attach an OH with a single line to the carbon.  The OH (called the hydroxyl group) can be attached to either the right-side carbon, or the left side carbon, it makes no difference.

In general, the LONGER a hydrocarbon chain, the higher the boiling point.  The boiling point is sometimes called vaporization point.  There are charts to compare and list boiling points of tens of thousands of substances; google "Boiling point ether" and "Boiling point ethanol" and see what comes up.  You can also google "MSDS Ethanol" and "MSDS dimethyl ether" and see what happens when you type those phrases in.  (Scroll down to physical properties).  I don't think you need to use elaborate formulas to arrive at a substances boiling point, as you will need to know it's molar entropy of vaporization AND its molar mass, then do a couple of calculations.