# Elevated boiling points in alkanes with even number of carbons [duplicate]

Why do alkanes with even number of carbon atoms have greater boiling points than those with odd number of carbon atoms?

## marked as duplicate by ringo, Todd Minehardt, Jon Custer, Freddy, bonApr 24 '16 at 19:15

• Because there is always a heavier alkane with equal number of carbon atoms than one with an odd number of carbon atoms. – aventurin Apr 23 '16 at 17:26

There is not really any difference between the boiling points of even and odd carbon alkanes. For single-chain alkanes the boiling point just goes up as a smooth curve versus chain length.

The melting points do show a small oscillating component with the even chains being higher. If we imagine the chains in their idealized zig-zag configuration, which would be relatively favorable for the solid state, we find that the even-length chains have a center of inversion which makes them fit better than odd-length ones. This effect fades, however, with increasing chain length.

Reference:

https://en.wikipedia.org/wiki/Alkane

I think you asked your question poorly. Here is data from Wikipedia. Most of the BP's were given as ranges. I rounded some and some I took the average. But in all cases as the number of carbons increases, the BP increases.

 alkane        #Carbons   B.P. (°C)
methane          1       −161.49
ethane           2        −88.5
propane          3        −42.2
n-butane         4          0
n-pentane        5         36
n-hexane         6         69
n-heptane        7         98
n-octane         8        125
nonane           9        151
decane          10        174
undecane        11        195
dodecane        12        216


I also fit the data to a 3rd order polynomial.

BP=-2.262586E+002 + 7.517034E+001*C - 5.350278E+000*C^2 + 1.810153E-001*C^3

    alkane    #Carbon  BP(data)   BP(fit)  error
methane     1        -161.5   -156.3    5.2
ethane      2         -88.5    -95.9   -7.4
propane     3         -42.2    -44.0   -1.8
n-butane    4           0.0      0.4    0.4
n-pentane   5          36.0     38.5    2.5
n-hexane    6          69.0     71.3    2.3
n-heptane   7          98.0     99.9    1.9
n-octane    8         125.0    125.4    0.4
nonane      9         151.0    148.9   -2.1
decane     10         174.0    171.4   -2.6
undecane   11         195.0    194.2   -0.8
dodecane   12         216.0    218.1    2.1


Here is a plot of the residuals. As Oscar Lanzi indicated there is no evidence of an even-odd trend.