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Physical Properties of Organic Compounds

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Introduction

Physical Properties of Organic Compounds 1) Explain the differences in boiling points between the straight chain alkanes. Since straight change alkanes experience van der Waal (London ) forces, the higher the number of carbons in the straight chain alkane, the higher the boiling point, as more carbons contributes to stronger and more forces. 2) Explain the differences in boiling points between the straight and branched chain alkane. The difference in boiling points between straight and branched alkanes can be explained by the decrease in dipole moments due to a shorter chain length in branched alkanes. 0 3) What is the functional group in alcohol? The functional group in alcohols is the hydroxyl group -OH. 4) Explain the differences in the boiling points between similar massed short chain(<5 C) alcohols and alkanes. Alkanes, have much lower boiling points then similar massed short chained alcohols due to its ability to form hydrogen bonds. Since hydrogen bonds are significantly stronger than London forces, it would take more heat to boil them. Hence the alcohol would have a much higher boiling point than the alkane. ...read more.

Middle

An OH bond is more polar than a NH bond because oxygen has a higher electronegativity than nitrogen, resulting in a higher electronegativity difference between the OH bond, which means oxygen has a greater pull on the electrons than nitrogen does in their respective bonds. Hence the OH bond is polar. 12) Draw the H-bonding possible for Ammonia (NH3) 13) Are mono, di and tri substituted amines capable of H-bonding? Mono substituted amines are possible of hydrogen bonding (between the lone pair of the very electronegative of the nitrogen and the slightly positive hydrogen of another molecule) , as our di substituted amines. However, tri substituted amines are not capable of hydrogen bonding. 14) Compare the boiling points between ethane, methylamine and methanol. Explain. Between ethane and methylamine, methylamine has the higher boiling point despite both having the same number of electrons. This is due the fact that methylamine is able to form a hydrogen bond with another methylamine molecule which ethane is unable to do so. ...read more.

Conclusion

Explain. The difference in boiling points of methoxymethane and ethanol is that ethanol has a hydrogen atom attached directly to an oxygen and so hydrogen bonding can occur between ethanol molecules. However, in methoxymethane, there aren't enough hydrogens for hydrogen bonds to form. Hence the boiling point of ethanol is significantly higher. The same concept can be applied to comparing methoxyethane with propanol. 22) Compare the cis to trans- 2-butene isomers and pentane to neopentane. Explain the differences in boiling and melting points. Between the cis and trans isomers 23) Compare the structures of cis-1,2-dichloroethene and trans - 1,2 -dichloroethene. Explain the differences in boiling and melting points The difference between the two can be explained by the fact that in cis form, there are 2 polar C-Cl dipole moments, giving an overall molecular dipole and so when it bonds with other molecules, there are dipole-dipole forces as well as London dispersion which increases the boiling point. However, in the trans form, the two C-Cl bond moments cancel and the molecule is rendered non-polar and so there are no dipole-dipole forces involved hence a lower boiling point. ?? ?? ?? ?? November 14, 2009 Sanjana Negi ...read more.

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