As more carbons are added to a carboxylic acid, the trend indicates that the boiling point increases. The main functional group in a carboxylic acid (COOH) leads to strong bonds to start off with.
The functional group (COOH) comes from combines the forces of a carbonyl group (polar covalent bonds, London forces, and dipole dipole forces) with the forces of an even stronger group, an alcohol (polar covalent bonds, London forces, dipole dipole forces, and hydrogen bonds) creating a very strong functional group.
This group proves to need the most energy to be broken down, thus hit its boiling point which explains why the points for carboxylic acids are greater than those of the other functional groups. As the number of carbons is increased, the number of electrons and protons also increases, thus creating a greater amount of London force. This greater amount of London force indicates more energy is needed to break its intermolecular bonds, thus it having a higher boiling point than its predecessor.
The slight increase between butanoic acid and pentanoic acid can be explained by the size of the molecules. As the molecule starts to increase in size, more London forces are added, but other stronger intermolecular forces are weakened. The weakening of the hydrogen and dipole-dipole forces enables the molecule to only slightly increase its boiling point.
In general, chloroalkanes contain lower boiling points than alcohols. This can be explained by looking at the intermolecular forces of both organic compounds. Chloroalkanes only contain London and dipole-dipole forces, while alcohols contain these two intermolecular forces, plus the very strong hydrogen bonding.
Because of the extra intermolecular force (hydrogen bonds), it takes more energy to break the bonds of an alcohol which explains its higher boiling point. As the molecule gets larger, London forces are added but the other forces are weakened because of the large size of the molecule. This explains why it seems like chloroalkanes are ‘catching up’ to the alcohols in the later stages of the graph.
Alkanes: This type of organic compound contains only the weakest intermolecular force, London forces and therefore has the lowest boiling point. As carbons get added onto an alkane, London forces are greatly increased because many protons and electrons are being added. The addition of only London forces allows for such a range each time a carbon (accompanied by 3 hydrogens) is added, which explains the long intervals in the graph
Chloroalkanes: Chloroalkanes contain a higher boiling point than alkanes because they not only contain London forces, but also dipole dipole forces as their intermolecular forces. The addition of these dipole dipole forces enables chloroalkanes to have a higher boiling point than alkanes.
The range of boiling points for chloroalkanes is quite great. It stretches from -24 to 259 degrees Celsius. As carbons are added, the boiling point increases because of the addition of London forces. Because of the dipole dipole forces, the range in between values is not as great as they are for alkanes. The strength of the dipole dipole forces is the reason for this smaller range.
Alcohols: Alcohols contain three types of intermolecular bonds, London bonds, dipole dipole bonds and hydrogen bonds. The addition of the very strong hydrogen bonds increases the alcohols boiling point substantially.
Alcohols have a greater boiling point, which leads to them having a smaller range in temperature between points. The addition of London forces does less to alcohols because they contain three types of intermolecular forces, rather than only London or London and dipole dipole.
Ethers: Ethers contain both London forces and dipole dipole forces which enables the range to be less than alkanes. Since they contain both dipole dipole and London forces, the boiling point is higher than alkanes and roughly the same as both chloroalkanes and aldehydes.
The range changes slightly more than alkanes but less than the compounds with hydrogen bonds. The London forces and dipole dipole forces enable a smaller range than alkanes.
Aldehydes: Aldehydes contain London forces and dipole dipole forces making them similar to ethers and chloroalkanes. The polar part of this molecule is in the middle rather than at the end, but still acts in the same manner. Their boiling point is higher than alkanes but lower than alcohols, because they do not contain hydrogen bonding.
As London forces are added (carbons) the range is not affected as much as alkanes because of their dipole dipole forces, but affected more than the range of alcohols (because of their hydrogen bonds).
Carboxylic Acids: Carboxylic acids contain the highest boiling points out of the organic compounds covered. The combination of the forces from a carbonyl and the alcohol to produce the COOH enables it to have the strongest intermolecular forces (London forces, dipole dipole and hydrogen bonding) which in turn indicate the highest boiling point.
The range varies the least in this compound, because it contains the strongest bonds. The addition of London forces (carbons) does not act on these compounds as much as they would those with weaker intermolecular forces (alkanes, chloroalkanes, ethers, aldehydes, and alcohols).
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