HS Chemistry - Carbonyl Functional Groups

Unit Summary

Aldehydes

• Aldehydes are a type of carbonyl functional group with the formula RCHO, where R represents the rest of the molecule before the CHO.

• In an aldehyde, the CHO group is found at the end of the main chain. Therefore, it is not necessary to note the position of the CHO group with a number, as the numbering of the main chain will start from the end with the CHO group.

• A aldehyde's name is found by taking the name of the rest of the molecule and adding "-al" to the end.

• If an aldehyde group is present in an organic molecule, the molecule will be classified as an aldehyde, even if other functional groups are present, unless one of the other functional groups present has a higher precedence than the aldehyde functional group.

• A molecule with two aldehyde groups is called a dialdehyde. Its suffix is "-dial", and its main chain is the longest Carbon chain that connects both CHO groups.

• Since the aldehyde group takes precedence over the hydroxyl $OH$ group, organic molecules with both hydroxyl groups and aldehyde groups are classified as aldehydes.

  • The suffix is "-al" $or "\-dial" if it is a dialdehdye$.
  • The hydroxyl group is added to the prefix of the organic molecule with the prefix "hydroxy", with a number noting the hydroxyl group's position. The numbering starts from the end with the aldehyde group.

• If there are multiple possible main chains, then the one with the most aldehyde groups will be the main chain. If there are multiple possible main chains with the same amount of aldehyde groups, then the one with the most Carbon atoms will be the main chain.

• When an aldehyde is attached to a cycloalkane or arene, the suffix "-aldehyde" is used, with a prefix like "di-" or "tri-" appended to the beginning of the suffix to indicate how many aldehyde groups are present. Additionally, the aldehyde groups are numbered.

• There are two ways to form aldehydes:

  • Oxidizing an alkene using hot, concentrated acidified potassium permanganate $KMnO~4~$ solution. This requires that one of the Carbons in the double bond is bonded to one Hydrogen atom and one other non-Hydrogen atom $typically a Carbon atom$.
  • Oxidizing a primary alcohol using hot, concentrated acidified potassium permanganate $KMnO~4~$ solution or hot, concentrated acidified potassium dichromate $K~2~Cr~2~O~7~$ solution.
  • The aldehyde must be distilled off to the side as it is being formed to prevent it from being further oxidized into a carboxylic acid.
  • If KMnO₄ is used, the KMnO₄ solution will lose its purple color and become colorless. If K₂Cr₂O₇ is used, the K₂Cr₂O₇ solution will turn from an orange color to a green color.

• Reducing an aldehyde will yield a primary alcohol.

  • If NaBH₄ is used as the reducing agent, the aldehyde must be heated with a solution of NaBH₄ dissolved in water.
  • If LiAlH₄ is used as the reducing agent, the LiAlH₄ must be dissolved in a dry ether at room temperature before being added to the aldehyde.

• Aldehydes can undergo addition reactions with hydrogen cyanide $HCN$. In this reaction, the C=O bond in the aldehyde is broken, and the Carbon atom that was previously double-bonded to the Oxygen atom is now bonded to a hydroxyl group $OH$ and a nitrile group $C≡N$.

  • HCN is a very toxic gas, so instead of being added directly, it is produced in the reaction apparatus by reacting another cyanide, like KCN, with an acid.
  • The product molecule is a type of 2-hydroxynitrile molecule.

  • This reaction increases the length of the organic molecule's main chain by one Carbon atom.

  • After the nitrile is formed, it can:

    • Undergo hydrolysis with a dilute solution of HCl under reflux to become a carboxylic acid.
    • Be reduced by sodium and ethanol to an amine $a different functional group$.
    • In both these reactions, most of the organic molecule is left unchanged, and only the functional group at the end of the organic molecule is different.

• 2,4-DNPH solution $Brady's reagent$ can be added to an organic compound in a test tube to see whether the organic compound is an aldehyde or ketone. If an orange precipitate forms, the organic molecule is either an aldehyde or ketone. If the solution remains green, the organic molecule isn't an aldehyde or ketone.

• Fehling's solution can be added to an organic compound in a test tube to see whether the organic molecule is an aldehyde. If it is, a red$ish$ precipitate will form.

  • Fehling's solution must be prepared directly before conducting the test, as Fehling's solution cannot be directly stored.

• Tollens' reagent, which consists of Silver nitrate in excess ammonia solution, can also be used to see if the organic molecule is an aldehyde. If it is, the Silver ions will oxidize and form a mirror inside the test tube.

Ketones

• Ketones are a type of carbonyl functional group with the formula R₁COR₂, where R₁ represents the rest of the molecule before the carbonyl $C=O$ group, and R₂ represents the rest of the molecule after the carbonyl group.

• In a ketone, the functional group is not found at the end of the main chain. Therefore, it is necessary to note the position of the ketone functional group with a number.

• A ketone's name is found by taking the name of the rest of the molecule and adding "-one" to the end.

• If a ketone group is present in an organic molecule, the molecule will be classified as a ketone, even if other functional groups are present, unless one of the other functional groups present has a higher precedence than the ketone functional group.

• A molecule with two ketone groups is called a diketone. Its suffix is "-dione", and its main chain is the longest Carbon chain that connects both ketone functional groups. This extends to triketones and further on, but they are not expected to be encountered at this level.

• Since the ketone group takes precedence over the hydroxyl $OH$ group, organic molecules with both hydroxyl groups and ketone groups are classified as ketones.

  • The suffix is "-one" $or "\-dione" if it is a diketone$.
  • The hydroxyl group is added to the prefix of the organic molecule with the prefix "hydroxy", with a number noting the hydroxyl group's position. The numbering starts from the end that gives the ketone group the smallest number.

• If there are multiple possible main chains, then the one with the most ketone groups will be the main chain. If there are multiple possible main chains with the same amount of ketone groups, then the one with the most Carbon atoms will be the main chain.

• There are also organic molecules with both aldehyde and ketone functional groups:

  • The aldehyde group takes precedence over the ketone group, and the molecule is classified as an aldehyde. Thus, the suffix is "-al" $or "\-dial" if it is a dialdehyde$, and the numbering starts from the end with the aldehyde group.
  • The ketone group is noted in the prefix as "oxo", with a number noting the hydroxyl group's position.

• There is a common naming system $common is part of the name$ for ketones.

  • The common name for ketones is formed by taking the names of the two groups attached to the C=O bond in the ketone, ordering them alphabetically, and appending the word "ketone" at the end $e.g. ethyl propyl ketone, ethyl methyl ketone, dimethyl ketone, etc.$.
  • Ketones are often categorized through the common naming system. For example, any ketone with a methyl group on one side is considered a methyl ketone $e.g. methyl propyl ketone, butyl methyl ketone, dimethyl ketone, etc.$. Grouping ketones in this way using their common names can be very useful in identifying commonalities among different types of ketones.

• When a ketone is attached to a cycloalkane or arene, the suffix "-one" is used, with a prefix like "di-" or "tri-" appended to the beginning of the suffix to indicate how many aldehyde groups are present. Additionally, the aldehyde groups are numbered.

• There are two ways to form ketones:

  • Oxidizing an alkene using hot, concentrated acidified potassium permanganate $KMnO~4~$ solution. This requires that one of the Carbons in the double bond is bonded to two non-Hydrogen atoms $typically Carbon atoms$.
  • Oxidizing a secondary alcohol using hot, concentrated acidified potassium permanganate $KMnO~4~$ solution or hot, concentrated acidified potassium dichromate $K~2~Cr~2~O~7~$ solution.
  • The ketone does not need to be distilled off to the side as it is being formed, as it will not be further oxidized into another substance.
  • If KMnO₄ is used, the KMnO₄ solution will lose its purple color and become colorless. If K₂Cr₂O₇ is used, the K₂Cr₂O₇ solution will turn from an orange color to a green color.

• Reducing a ketone will yield a secondary alcohol.

  • If NaBH₄ is used as the reducing agent, the ketone must be heated with a solution of NaBH₄ dissolved in water.
  • If LiAlH₄ is used as the reducing agent, the LiAlH₄ must be dissolved in a dry ether at room temperature before being added to the ketone.

• Ketones can undergo addition reactions with hydrogen cyanide $HCN$. In this reaction, the C=O bond in the ketone is broken, and the Carbon atom that was previously double-bonded to the Oxygen atom is now bonded to a hydroxyl group $OH$ and a nitrile group $C≡N$.

  • HCN is a very toxic gas, so instead of being added directly, it is produced in the reaction apparatus by reacting another cyanide, like KCN, with an acid.
  • The product molecule is a type of 2-hydroxynitrile molecule.
  • This reaction increases the length of the organic molecule's main chain by one Carbon atom.

  • After the nitrile is formed, it can:

    • Undergo hydrolysis with a dilute solution of HCl under reflux to become a carboxylic acid.
    • Be reduced by sodium and ethanol to an amine $a different functional group$.
    • In both these reactions, most of the organic molecule is left unchanged, and only the functional group at the end of the organic molecule is different.

• 2,4-DNPH solution $Brady's reagent$ can be added to an organic compound in a test tube to see whether the organic compound is an aldehyde or ketone. If an orange precipitate forms, the organic molecule is either an aldehyde or ketone. If the solution remains green, the organic molecule isn't an aldehyde or ketone.

• Fehling's solution can be used in combination with 2,4-DNPH solution to see if an organic molecule is a ketone.

  • If it forms an orange precipitate with 2,4-DNPH solution, the organic compound is either an aldehyde or ketone.
  • A sample of the organic compound can then be placed in a separate test tube, and Fehling's solution can be added to it. If a red precipitate doesn't form, then the organic compound isn't an aldehyde. Since it formed an orange precipitate with 2,4-DNPH solution, it must be a ketone.
  • Fehling's solution must be prepared directly before conducting the test, as Fehling's solution cannot be directly stored.

• Tollens' reagent, which consists of Silver nitrate in excess ammonia solution, can also be used in combination with 2,4-DNPH solution to see if the organic molecule is a ketone.

  • If it forms an orange precipitate with 2,4-DNPH solution, the organic compound is either an aldehyde or ketone.
  • A sample of the organic compound can then be placed in a separate test tube, and Tollens' reagent can be added to it. If Silver ions don't oxidize and a mirror isn't formed inside the test tube, then the organic compound isn't an aldehyde. Since it formed an orange precipitate with 2,4-DNPH solution, it must be a ketone.

Carboxylic Acids

• Carboxylic acids are a type of carbonyl functional group with the formula RCOOH, where R represents the rest of the molecule before the COOH.

• In a carboxylic acid, the COOH group is found at the end of the main chain. Therefore, it is not necessary to note the position of the COOH group with a number, as the numbering of the main chain will start from the end with the COOH group.

• A carboxylic acid's name is found by taking the name of the rest of the molecule and adding "-oic acid" to the end.

• Carboxylic acids have the highest priority of any functional group. Therefore, if a carboxylic acid group $COOH$ is present, the organic molecule will be classified as a carboxylic acid, even if other functional groups are present.

• A molecule with two carboxylic acid groups is called a dicarboxylic acid. Its suffix is "-dioic acid", and its main chain is the longest Carbon chain that connects both COOH groups.

• If there are multiple possible main chains, then the one with the most COOH groups will be the main chain. If there are multiple possible main chains with the same amount of COOH groups, then the one with the most Carbon atoms will be the main chain.

• If a hydroxyl group is present in a carboxylic acid, it is noted in the prefix as "hydroxy-", with a number to indicate its position in the molecule. If a ketone is present in a carboxylic acid, it is noted in the prefix as "oxo-", with a number to indicate its position in the molecule.

• When a carboxylic acid is attached to a cycloalkane or arene, the suffix "-carboxylic acid" is used, with a prefix like "di-" or "tri-" appended to the beginning of the suffix to indicate how many carboxylic acid groups are present. Additionally, the carboxylic acid groups are numbered.

• Carboxylic acids are formed by oxidizing an aldehyde with acidified KMnO₄ solution or acidified K₂Cr₂O₇ solution. The reaction is carried out in a reflux vessel.

  • If we start off with an alkene or primary alcohol and oxidize that into an aldehyde first, we don't distill the aldehyde off to the side, but instead keep it in the reaction vessel to further oxidize it into a carboxylic acid.
  • If KMnO₄ is used, the KMnO₄ solution will lose its purple color and become colorless. If K₂Cr₂O₇ is used, the K₂Cr₂O₇ solution will turn from an orange color to a green color.

• Carboxylic acids can also be formed when a nitrile undergoes hydrolysis with a slightly acidic or basic solution under reflux.

• When an ester undergoes hydrolysis with an acid catalyst, a carboxylic acid is formed.

• Reducing a carboxylic acid with LiAlH₄ will yield a primary alcohol.

• Carboxylic acids can be used to make esters.

• Since carboxylic acids are acids, they can participate in the same reactions as other acids.

• When a carboxylic acid reacts with a base, it will produce a carboxylate salt. Thus, if a compound that is known to contain some type of carbonyl functional group reacts with a base, it is a carboxylic acid. This can be used to test for the presence of carboxylic acids. Carboxylates have the suffix "-oate".

Esters

• Esters are a type of carbonyl functional group with the formula R₁COOR₂, where R₁ represents the rest of the molecule before the carbonyl $C=O$ group, and R₂ represents the rest of the molecule after the carbonyl $C=O$ group.

• An ester is formed by reacting a carboxylic acid with an alcohol using an acid catalyst $usually concentrated H~2~SO~4~$. This process is known as esterification.

  • Esterification is carried out in a reflux apparatus to prevent the reactants from evaporating and escaping.

• Esterification is a type of condensation reaction, where the hydroxyl group $OH$ from the alcohol combines with the Hydrogen atom from the carboxylic acid's COOH group to form H₂O, and the rest of the two molecules combine at the ends where the hydroxyl group and Hydrogen atom formerly were.

• An ester's name consists of two parts:

  • The first part of the name comes from the alcohol that was used to make the ester. It is named were a side chain, based on how many Carbon atoms are in this part $methyl\-, ethyl\-, etc.$. The numbering for both parts is separate, and for this part, it starts from the Carbon atoms after the Oxygen atoms, not from the beginning of the ester.
  • The second part of the name comes from the carboxylic acid that was used to make the ester, and is named like a carboxylate compound $i.e. the suffix is "\-oate", and the parent part of the name denotes the number of Carbon atoms in the carboxylic acid's main chain$.

• Esters can undergo a hydrolysis reaction to reverse the esterification process, producing a carboxylic acid and alcohol when an acid catalyst is used.

  • Since this uses an acid catalyst and produces a carboxylic acid and alcohol, the carboxylic acid and alcohol can then undergo esterification with the acid catalyst to produce the ester and H₂O, which can then undergo hydrolysis to yield a carboxylic acid and alcohol, and so on. Thus, this reaction is reversible.

• When an ester undergoes a hydrolysis reaction with a base, the reaction is irreversible, as a carboxylate salt and alcohol are produced instead of a carboxylic acid and alcohol, and the carboxylate salt and alcohol can't be reacted together to yield the ester and base.