[Chemistry Class Notes] on Ketone General Molecular Formula Pdf for Exam

The presence of a carbonyl group in which the carbon atom is covalently bound to an oxygen atom distinguishes ketone from other organic molecules. Other carbon atoms or hydrocarbon radicals form the remaining two bonds.

This article will study the formula of ketone and ketone structure in detail.

Reactivity of Ketone Due to Ketone Structure 

Because oxygen is significantly more electronegative than carbon, it has a significant potential to attract electrons from a carbon-oxygen bond. One of the two pairs of electrons in a carbon-oxygen double bond is more easily attracted to the oxygen. As a result, the carbon-oxygen double bond is extremely polar. 

Given Below is the Ketone Structure:

The above ketone structural formula shows that:

Nucleophiles can attack the somewhat positive carbon atom in the carbonyl group. A nucleophile is a negatively charged ion (such as the cyanide ion, CN–) or a slightly negatively charged component of a molecule (for example, the lone pair on a nitrogen atom in ammonia, NH3).

The carbon-oxygen double bond is broken during the process. All of this results in the carbonyl group undergoing additional reactions, which are frequently followed by the loss of a water molecule. This results in an addition-elimination or condensation process. If you look through the aldehydes and ketones menu, you’ll discover instances of simple addition reactions and addition elimination. A carbonyl group can be found in both aldehydes and ketones. That is to say, their responses are remarkably comparable in this regard.

Nomenclature of Ketones

According to ketone chemical formula or ketone molecular formula:

The International Union of Pure and Applied Chemistry (IUPAC) name of a ketone is derived by choosing the longest chain of carbon atoms containing the carbonyl group as the parent. The carbonyl carbon is the smaller number in the parent chain, which is counted from the end. To indicate that the molecule is a ketone, the parent alkane’s suffix -e is replaced with -one.

5-methyl-3-hexanone, for example, is designated CH3CH2COCH2CH(CH3)2. The longest chain has six carbon atoms, thus carbon numbering must begin at the end, giving the carbonyl carbon the smaller number. Carbon 3 has the carbonyl group, whereas carbon 5 has the methyl group. The numbering of the atoms in the ring in cyclic ketones starts with the carbonyl carbon as number 1. Ketones are given common names by separating each carbon group bound to carbon into its own word and then adding the word “ketone” to the end.

The most basic ketone, CH3COCH3, is nearly always referred to by its common name, acetone, which is derived from the fact that it was initially synthesised by heating the calcium salt of acetic acid.

Reactions of Ketone

Ketones are extremely reactive, but not as much as aldehydes, with which they share a close relationship. The nature of the carbonyl group is responsible for much of its chemical activity. Ketones are easily reacted within a wide range of chemical reactions. The carbonyl group is extremely polar, which means it has an unequal distribution of electrons. This is one of the main reasons. The carbon atom now has a partial positive charge, making it vulnerable to assault by nucleophiles, which are organisms that are attracted to positively charged centres. Oxidation-reduction and nucleophilic addition are two common processes. The physical properties of ketones are also affected by the polarity of the carbonyl group.

1. Secondary alcohols (R2CHOH R2CO) are quickly reduced to ketones. Because ketones are often resistant to additional oxidation, the reaction can be stopped at the ketone stage. Many oxidising agents can convert a secondary alcohol to a ketone, the most common of which being chromic acid (H2CrO4), pyridinium chlorochromate (PCC), potassium permanganate (KMnO4), or manganese dioxide (MnO2). The oxidation of ketones is not synthetically beneficial, with a few exceptions (such as the oxidative cleavage of cyclohexanone, C6H10O, to adipic acid, HO2C[CH2]4CO2H, a molecule used to produce nylon-6,6).

2. An aromatic hydrocarbon is converted to an aryl alkyl or diaryl ketone (ArH ArCOR or ArCOAr′) by reacting it with an acyl halide or anhydride in the presence of a Lewis acid (i.e., a substance capable of accepting an electron pair), most often aluminium chloride (AlCl3). Friedel-Crafts acylation is the name for this reaction.

3. Following hydrolysis (RCN + R′MgX RCOR′), nitriles (RCN) react with Grignard reagents to form ketones (RCN + R′MgX RCOR′).

4. Certain strategies can be used to get ketones with -hydrogens to undergo aldol reactions (also known as aldol condensation). When one carbon gives the carbonyl group and another gives the carbon with a -hydrogen, the reaction is commonly employed to close rings. The synthesis of 2-cyclohexenone is an example. In this case, the aldol product loses H₂O, resulting in an,-unsaturated ketone.

Physical Properties of Ketone

Boiling Point

Ketones are liquids with increasing boiling temperatures as the molecules become larger. The intensity of the intermolecular forces determines the size of the boiling point.

Van der Waals dispersion forces: As molecules get longer and have more electrons, these attractions become stronger. The size of the temporary dipoles that are set up grows as a result of this. This is why, as the number of carbon atoms in the chains grows, the boiling points rise.

Attractions of the van der Waals dipole-dipole: Because of the presence of the carbon-oxygen double bond, both ketones are polar compounds. There will be attractions between the permanent dipoles on neighbouring molecules in addition to the dispersion forces. This means that the boiling temperatures of similar-sized hydrocarbons, which solely have dispersion forces, will be greater. It’s fascinating to compare three molecules of similar size. They have similar lengths and quantities of electrons (albeit not identical).

Conclusion

Ketone is distinguished from other organic molecu
les by the presence of a carbonyl group in which the carbon atom is covalently bonded to an oxygen atom. The remaining two bonds are formed by other carbon atoms or hydrocarbon radicals.

Because oxygen is far more electronegative than carbon, it has a large potential for attracting electrons from a carbon-oxygen bond. In a carbon-oxygen double bond, one of the two pairs of electrons is more easily attracted to oxygen. As a result, the double bond between carbon and oxygen is very polar.