A functional group is an atom or group of atoms inside a molecule that exhibits comparable chemical properties across several molecules. Even if the rest of the molecule is very different, certain functional groups behave in predictable ways.
Organic molecules vary widely in size, and while studying functional groups, we want to focus on the atoms involved. As a result, the abbreviation R is employed in certain cases.
In molecular structures, the letter R represents the "rest of the molecule". It is made up of a collection of carbon and hydrogen atoms of various sizes. It is used as a shorthand since the addition of a group of carbon and hydrogen atoms has no effect on the compound's functioning. In some compounds, the letters R, R', or R'' indicate that the R groups in the molecule might differ from one another. For example, R may be -CH2CH3, but R' could be -CH2CH2CH2CH3.
Alkenes and Alkynes
Alkenes are hydrocarbons with one or more double bonds between adjacent carbon atoms. Alkynes have one or more triple bonds that connect nearby carbon atoms. The existence of a double or triple bond causes reactivity not found in alkanes, and alkynes experience specific reactions that will be discussed later.
Aromatic:
Benzene rings (C6H6) are a unique form of hydrocarbon. Benzene and its derivatives have historically been referred to as aromatic substances due to their distinct scent (sweet smell). The structure of benzene can be represented as three C=C double bonds alternating with single bonds; however, the real structure of benzene is unrelated to alkenes. Organic Chemistry II will go into detail on the structure of benzene, which is a large conjugation system, as well as the chemistry definitions of aromatic/aromaticity.
Alkyl halide (or haloalkane) is the group formed when a halogen is linked to carbon. The halide can be classified as primary (1°), secondary (2°), or tertiary (3°) based on the carbon linked to the halogen.
Alcohol:
The alcohol functional group consists of one oxygen atom linked to one hydrogen and one carbon atom. The carbon atom will form part of a bigger organic structure. The formula R−OH can imply a generic alcohol. R denotes any organic fragment in which a carbon atom is directly attached to the expressly specified functional group (OH in this case). The R group is usually a chain of carbon atoms.
Primary, secondary, and tertiary alcohols are categorized according to the characteristics of the carbon atom they are attached to. The carbon that is directly attached to the oxygen atom in a primary alcohol is likewise bonded to only one carbon atom, with the other connections frequently going to hydrogen atoms. The carbon atom is bound to two other carbon atoms in a secondary alcohol and to three other carbon atoms in a tertiary alcohol. The results of particular reactions will depend on the type of alcohol utilized. The number of the carbon to which the −OH group is connected indicates where it is located. We already know a few common types of alcohol. For instance, the alcohol found in alcoholic beverages is called ethanol (CH3CH2OH). It is extensively employed in the industrial production of other compounds as well. Methanol (CH3OH) is a substitute or addition for gasoline. Furthermore, formaldehyde, which is needed to make paints, polymers, and other valuable compounds, can be made from methanol. Rubbing alcohol is a frequent name for isopropanol.
Ether:
Ether is another functional group in which the oxygen atom is present in single bonds. Two C-O σ bonds allow the O atom in ether to link with two R groups that contain carbon. "Alkyl alkyl ether" is the typical term for compounds in which ether is the only functional group. The term "dialkyl" refers to the combination of two identical alkyl groups. Ether is also capable of having a cyclic structure.
Amine:The organic form of ammonia, NH3, is called an amine. Amine is created when R groups are added to the hydrogen atom(s) in NH3. Primary (1°), secondary (2°), or tertiary (3°) amino acids can be found, depending on how many R groups are attached to nitrogen. Nitrogen atoms are present in both nitrile and nitro groups, and they are interchangeable. Nitro (NO2) can be anywhere on the carbon chain or ring, whereas nitrile (Nitrile) can only be at the end of structure due to its C-N triple bond.
Because the lone pair on nitrogen can function as a proton acceptor, neutral amines are weak bases. The smells of many minor amines are overpowering and unpleasant. Cadaverine and putrescine, for instance, are noxious-smelling amines that are produced during the decomposition process following death.
Aldehydes
The carbonyl is a relatively frequent structural component of organic compounds, consisting of a carbon atom and an oxygen atom joined by a double bond. Carbonyls' reactivity is mostly determined by the polarization of the C=O bond, although the surrounding atoms also contribute to their unique reaction pathways. Carbonyl, while a component of many functional groups, is not a functional group in and of itself.
An aldehyde is a carbonyl containing at least one hydrogen atom. The additional group linked to the carbonyl could be an R-group or a hydrogen atom. Because the hydrogen atom is so tiny, other molecules can easily approach the partial positive charge on the carbonyl carbon, making aldehydes a highly reactive kind of carbonyl. Aldehydes are flexible reactants used in a wide range of chemical synthesis. Many aldehydes exhibit different smells and aromas.
A molecule in which two hydrogen atoms are linked to the carbonyl is called a peculiar aldehyde. Formaldehyde is a chemical that has many applications. It can be used as a very strong disinfectant or as a tissue preservative on its own. Additionally, it serves as a precursor for a number of materials, such as resins, plastics, and other polymers.
Ketone:
A carbonyl, or ketone, is a compound in which two RR-groups form single bonds with the carbon atom. Although they are often less reactive than aldehydes, ketones go through most of the same processes. Acetone, in which the carbonyl carbon is linked to two CH3CH3 groups, is the most basic ketone. This ketone is used as an industrial solvent and frequently used to remove nail polish. Methyl ethyl ketone finds applications as a solvent and paint remover. Additionally, ketones are employed as a solvent or as a building block in the synthesis of certain polymers.
The structures and chemical characteristics of the final four functional groups are connected. The entire COOH molecule is referred to as a carboxylic acid functional group when an OH group is joined to C=O. Since the other three—amide, anhydride, and ester—are all derivatives of carboxylic acid, carboxylic acid can be used as the raw material in their preparation. It's crucial to keep in mind that, for these three functional groups, the "W" component and C=O must be taken into account jointly because, taken together, they define the functional group.