Alkane boiling points

Alkane boiling points. The boiling points of the unbranched alkanes (blue) are compared with those of some branched alkanes (green). Because of their smaller surface areas, branched alkanes have lower boiling points than unbranched alkanes. 

Randic, M. and Trinajstic, N. (1994). Isomeric Variations in Alkanes Boiling Points of Nonanes. NewJ.Chem., IS, 179-189. 

Ivanciuc, O. (1998c) Artificial neural networks applications. Part 9. MolNet prediction of alkane boiling points. Rev. Roum. Chim., 43, 885-894. 

Figure 1 5.7 Boiling points of the first 10 unbranched alkanes. Boiling point increases smoothiy with chain iength because dispersion forces increase. Each entry inciudes the name, moiar mass (M, in g/moi), formula, and boiling point at 1 atm pressure.

Figure 1.18 Normal alkane boiling points depend on chain length.

M. Randic and N. Trinajstic, Isomeric variations in alkanes Boiling points of nonane, NewJ. Chem. 18 (1994) 179-189. 

C. How is the trend in alkane boiling points used in petroleum fractional distillation ... 

The first index based on a graph approach to molecular structure was developed by Wiener in 1947. The path number was defined as the number of bonds between all pairs of atoms in an acyclic molecule. Using the path number and another index, Wiener was able to fit alkane boiling points fairly well. The Wiener number is inversely proportional to the compactness of a molecule. In 1971 Hosoya connected the Wiener number with graph theory, pointing out that the Wiener number is the half-sum of all the distance matrix entries for a molecule. ... 

Their boiling points and densities are higher than alkanes having the same number of carbon atoms. 

FIGURE 2 12 Boiling points of unbranched alkanes and their 2 methyl branched iso mers (Temperatures in this text are expressed in de grees Celsius C The SI unit of temperature is the kelvin K To convert degrees Celsius to kelvins add 273 15 )... 

As noted earlier m this section branched alkanes have lower boiling points than their unbranched isomers Isomers have of course the same number of atoms and elec Irons but a molecule of a branched alkane has a smaller surface area than an unbranched one The extended shape of an unbranched alkane permits more points of contact for mtermolecular associations Compare the boiling points of pentane and its isomers... 

Match the boiling points with the appropriate alkanes Alkanes octane 2 methylheptane 2 2 3 3 tetramethylbutane nonane foiling points °C 1 atm) 106 116 126 151 ... 

Alkanes and cycloalkanes are nonpolar and insoluble m water The forces of attraction between alkane molecules are induced dipole/induced dipole attractive forces The boiling points of alkanes increase as the number of carbon atoms increases Branched alkanes have lower boiling points than their unbranched isomers There is a limit to how closely two molecules can approach each other which is given by the sum of their van der Waals radii... 

We have seen in this chapter that among isomenc alkanes the unbranched isomer is the least stable and has the highest boiling point the most branched isomer is the most stable and has the lowest boiling point Does this mean that one alkane boils lower than another because it is more stable" Explain... 

Boiling Point When describing the effect of alkane structure on boiling point m Sec tion 2 17 we pointed out that van der Waals attractive forces between neutral molecules are of three types The first two involve induced dipoles and are often referred to as dis persion forces or London forces... 

Table 4 2 lists the boiling points of some representative alkyl halides and alcohols When comparing the boiling points of related compounds as a function of the alkyl group we find that the boiling point increases with the number of carbon atoms as it does with alkanes... 

Alkynes resemble alkanes and aUcenes m their physical properties They share with these other hydrocarbons the properties of low density and low water solubility They are slightly more polar and generally have slightly higher boiling points than the corre spondmg alkanes and alkenes... 

The physical properties (boiling point solubility m water dipole moment) of alkynes resemble those of alkanes and alkenes... 

It IS instructive to compare the physical properties of ethers with alkanes and alcohols With respect to boiling point ethers resemble alkanes more than alcohols With respect to solubility m water the reverse is true ethers resemble alcohols more than alkanes Why" ... 

Hydrogen bonding m carboxylic acids raises their melting points and boiling points above those of comparably constituted alkanes alcohols aldehydes and ketones... 

Section 20 8 Esters are polar and have higher boiling points than alkanes of compa rable size and shape Esters don t form hydrogen bonds to other ester molecules so have lower boiling points than analogous alcohols They can form hydrogen bonds to water and so are comparable to alcohols m their solubility m water... 

We have often seen that the polar nature of a substance can affect physical properties such as boiling point This is true for amines which are more polar than alkanes but less polar than alcohols For similarly constituted compounds alkylamines have boiling points higher than those of alkanes but lower than those of alcohols... 

The only method utilized commercially is vapor-phase nitration of propane, although methane (70), ethane, and butane also can be nitrated quite readily. The data in Table 5 show the typical distribution of nitroparaffins obtained from the nitration of propane with nitric acid at different temperatures (71). Nitrogen dioxide can be used for nitration, but its low boiling point (21°C) limits its effectiveness, except at increased pressure. Nitrogen pentoxide is a powerful nitrating agent for alkanes however, it is expensive and often gives polynitrated products. 

Alkan olamines have high boiling points and under normal ambient conditions their vapor pressures are low. Only DMAMP (see Table 2) forms an azeotrope with water, which boils at 98.4°C and contains 25% by weight of DMAMP. According to current DOT regulations, AMP, AMP-95, DMAMP, DMAMP-80, AEPD, and AB are all classified as combustible Hquids. 

Heats of Vapon a/ion andFusion. A simple linear summation of most of the Lyderson groups (187) has been proposed for heat of vaporization at the normal boiling point and heat of fusion at atmospheric pressure for a wide variety of organic compounds (188). Average errors of 1.2 and 4.3% for group contribution-based estimations of heats of vaporization for selected n- and iso-alkanes, respectively, have been reported (215). 

Alkenes — Also known as olefins, and denoted as C H2 the compounds are unsaturated hydrocarbons with a single carbon-to-carbon double bond per molecule. The alkenes are very similar to the alkanes in boiling point, specific gravity, and other physical characteristics. Like alkanes, alkenes are at most only weakly polar. Alkenes are insoluble in water but quite soluble in nonpolar solvents like benzene. Because alkenes are mostly insoluble liquids that are lighter than water and flammable as well, water is not used to suppress fires involving these materials. Because of the double bond, alkenes are more reactive than alkanes. 

This will generally be tr-ue as we proceed to look at other alkanes as the number of carbon atoms increases, so does the boiling point. All the alkanes with four car bons or less are gases at room temperature and atmospheric pressure. With the highest boiling point of the three, propane is the easiest one to liquefy. We are all faniliar- with propane tanks. These are steel containers in which a propane-rich mixture of hydrocar bons called liquefied petroleum gas (LEG) is maintained in a liquid state under high pressure as a convenient clean-burning fuel. 

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