General Organic Chemistry (GOC) introduces students to the fundamental ideas of organic chemistry. A solid comprehension of the principles covered by General Organic Chemistry is essential for studying more advanced topics (such as the mechanisms of named reactions). Berzelius (1808) introduced the vital force theory and defined organic chemistry as the chemistry of chemicals contained in living matter. Wohler’s synthesis of urea, the first organic chemical synthesized in a laboratory, delivered a fatal blow to the vital force idea.
Organic compounds are hydrocarbons and their derivatives. Organic chemistry is the branch of chemistry that deals with these substances. Carbon typically catenates with four valence electrons, suggesting that it binds to itself, resulting in the formation of different compounds. Long chains of carbon atoms and hydrogens, such as dodecane, can be found, as can bands of carbon, such as anthracene, or complex structures of carbon and other atoms, such as the steroid estradiol.
Reasons for the large numbers of organic compounds
- Catenation: It is a self-combination tendency that is strongest in carbon. A carbon atom can form single, double, or triple bonds with other carbon atoms. As a result, it produces more compounds than the others.
- Tetravalency and small size of carbon: Carbon, as a tetravalent element, can form bonds with four additional C atoms or some other monovalent atoms. Carbon can combine with oxygen, hydrogen, chlorine, sulfur, nitrogen, and phosphorus to produce compounds. The type of the element or group linked to the carbon determines the properties of these compounds. Furthermore, due to the small size of carbon, these compounds are extremely stable.
General Properties of Organic Compounds
1. These are carbon compounds containing H, O, N, S, P, F, CI, Br, and I.
2. These are common in living beings. Carbohydrates, proteins, and so on.
3. These can be either gases, liquids, or solids.
4. Because they are covalent, they have a low boiling and melting point and are soluble in organic solvents.
5. These are often flammable and volatile.
6. Because there are no free ions, they do not conduct electricity.
7. They have a distinct color and aroma.
Terms involved in general organic chemistry
Nomenclature
The International Union of Pure and Applied Chemistry, or IUPAC, was founded in 1919 to bring the medical community together. This organization intended to ensure that chemists from all around the world could communicate successfully. There are now some general criteria for naming organic compounds. The most significant aspect of this method is that each molecular structure has only one IUPAC designation that corresponds to only one molecular structure.
The key features of the IUPAC system
- Only one name can be assigned to a given compound.
- The writing of a single chemical structure can be directed by a specified name.
- The approach is useful for naming complex organic substances.
- The approach is useful for naming multifunctional organic molecules.
- This is a straightforward, systematic, and scientific approach to organic compound nomenclature.
Any organic compound’s IUPAC name is composed of two or three elements.
- word root
- suffix
- prefix
The fundamental unit is a set of word roots that represent linear or continuous chains of atoms of carbon. The carbon chain with the greatest number of carbon is chosen as the root word.
Primary suffixes are added to root words to indicate saturation or unsaturation in a carbon chain.
Secondary suffixes are suffixes that are added after the primary suffix to indicate the existence of a certain functional group in the carbon chain.
Hybridization
S and p orbitals are involved in hybridization in organic or carbon molecules. This results in three types of hybridization: sp3(in alkanes), sp2(in alkenes), and sp (in alkayes). Generally, alkanes are tetrahedral in shape, alkenes are linear molecules, and alkynes are linear in shape.
Functional groups
The functional groups are the reactive groups present in compounds that determine the chemical properties of these compounds. Eg: -OH, -F, -CHO, -COOH.
Homologous series
A homologous series is a family of organic compounds with the same functional group, identical chemical characteristics, and successive members that differ in molecular formula by —CH2 units.
Members of a homologous series can be represented by the same general molecular formula.
Reaction mechanism of general organic chemistry
Effect mechanism maps that are easily detailed show us the paths we may require as well as noticeable problems along the way. In simple terms, an effect mechanism is a step-by-step sequence that lets us keep track of electron movements, bonds that form and break, and any molecules that arise on top of a chemical reaction. Generally, the reaction mechanism involves:
Reactants + Catalyst or Energy → Intermediate (Transition State) → Product
Appropriate reaction conditions assist in the production of a transition from the synthetic response between the reactants. These intermediates are often unstable, yet they react rapidly and provide a final product.
The reactants in a natural response are organized as follows:
Reagents are responsive compound species that initiate a response by attacking another species.
The substrate is the species that is attacked by the reagent in a natural response.
Depending on whether the reagent is electrophilic or nucleophilic, the area of reagent attack changes:
Electrophiles are electron-deficient entities that attack the substrate in an electron-rich region.
Nucleophiles are elements that have a lot of electrons and enjoy giving them away. Nucleophiles often attack the reagent at a low electron density region.
Bond cleavage in General Organic Chemistry
In most substance processes, existing compound bonds break down and new synthetic bonds are formed. There are two ways to break a covalent bond:
Homolytic Fission
It occurs when a covalent bond breaks off, leaving each molecule with one unpaired electron. Free radicals are complex compounds formed by homolytic fission. They are extremely sensitive (due to their unpredictable electron arrangements).
Heterolytic Fission
It occurs when a covalent bond breaks down to the point where one molecule retains two electrons while the other particle retains none. A component of heterolytic fission is the formation of a particle pair consisting of an effectively charged cation and an adversely charged anion.
Reaction intermediate involved in general organic chemistry
Heterolytic and homolytic bond fission produce short-lived fragments known as reaction intermediates. Carbonium ions, carbanions, carbon-free radicals, nitrenes, and carbenes are among the main chemical intermediates.
Free radicals
These are homolysis byproducts with an odd electron. With Sp2 hybridization, these are extremely reactive planar species.
Carbocations
Carbonium ions or carbocations are organic ions that contain a positively charged carbon atom. They are produced as a result of heterolytic bond fission. These are also planar chemical species, particularly sp2 hybridized with an empty p-orbital.
Carbanion
An organic ion with a negatively charged carbon atom is known as a carbanion. They are also produced as a result of heterolytic bond fission. These are pyramidal and made of Sp3 hybridized carbon (one lone pair).
Carbene
These are divalent carbon species with two bond pairs and two non-bonding electrons. These are produced via photolysis or pyrolysis.
The C-atom in singlet carbene is Sp2 hybridized. In these species, a hybridized orbital has no electrons, whereas a hybridized orbital has two electrons. Singlet carbene has a bent structure and is less stable than triplet carbene. The central C-atom in triplet carbene is sp-hybridized. Each sp – sp-hybridized orbital has one electron. The geometry of a triplet carbene is linear.
Nitrene
These are neutral monovalent nitrogen species having two unshared pairs of electrons on the N atom and a monovalent atom or group attached.
Some important topics of general organic chemistry
Inductive effect
In polar covalent compounds, it is comparable to changing a shared pair of electrons. When the shared pair is pushed more towards the more electronegative atom, the less electronegative atom gains a little positive charge while the more electronegative atom gains a partial negative charge. It is a permanent effect that spreads along the carbon chain. Atoms or groups with a higher electron affinity than hydrogen are said to have a negative inductive effect (- I), whereas those with a lower electron affinity than hydrogen are considered to have a positive inductive effect.
Hyperconjugation or no bond resonance
When an alkyl group is linked to an unsaturated system, such as the —CH=CH2 group, the order of the inductive action is reversed. The hyperconjugation effect helps explain the behavior. Such structures are formed by transferring bonding electrons from a neighboring C —H bond to the electron-deficient carbon. The positive charge that was originally on carbon is therefore transferred to hydrogen. The process of releasing electrons by assuming no bond character in the surrounding C—H bond is known as No-Bond Resonance or Hyperconjugation.
Electromeric effect
The term “electromeric effect” describes the polarity that results from a reagent attacking a compound with multiple bonds. When an electrophile E+ (a reagent) attacks a double or triple bond, the two Ï€ electrons from the bond are entirely transferred to one atom or the other. This is a temporary effect.
This can be of the + E type (when the electron pair is displaced away from the atom or group) or of the – E type (when the displacement is towards the atom or group).
Resonance effect
When a single structure cannot depict all of the features of a molecule and two or more structures are necessary, the structures are referred to as resonating structures or canonical forms, and the molecule is referred to as a resonance hybrid. This is referred to as resonance.
The resonance effect is a polarity created in a molecule by the interaction of two -bonds or a -bond and a lone pair of electrons on a neighboring atom. R and M effects are the two forms of resonance or mesomeric effects. Atoms that transfer electrons to a carbon atom are considered to have a +M or +R effect. The -M or -R effect refers to atoms or groups that attract electrons away from a carbon atom.
Isomerism
Isomerism occurs when two or more compounds have the same molecular formula but different structural formulas and differing physical and chemical characteristics. These chemicals are known as isomers.
There are two different types of isomerism:
Structural isomerism
Compounds with the same molecular formula but different structural formulae differ in the arrangement of atoms exhibit structural isomerism. Structural isomerism is further divided into various types. They are:
Chain isomerism: Chain isomers are isomeric compounds that differ solely in the arrangement of carbon atoms in the base chain, and chain isomerism refers to their isomeric connection.
Positional isomerism: Isomers have similar functional groups but are positioned at different places on the same carbon chain in position isomerism. This isomerism is often induced by functional groups attaching to different carbon atoms in the carbon chain.
Functional isomerism: Isomers with the same chemical formula but different functional groups are known as functional group isomers, and the process is known as functional group isomerism.
Metamerism: The relative position of alkyl groups surrounding polyvalent functional groups (such as S, N, O, and CO) in a molecule at different places causes this sort of isomerism. The existence of separate alkyl chains on each side of the functional group causes metamerism.
Stereoisomerism
Stereoisomerism occurs when isomers are generated by differing atomic or group configurations in space. The stereoisomers have the same structural formula but differ in how the atoms are arranged in space. It is further divided into different types:
Conformational isomerism
Stereoisomers can be interconverted in conformational isomerism by rotating around one or more single bonds, the bonds. These rotations provide non-superimposable atomic configurations in space.
Configurational isomerism
Stereoisomerism happens when different atomic or group configurations in space produce isomers. The stereoisomers have the same structural formula but differ in the arrangement of the atoms in space.
Geometrical isomerism
Geometrical isomerism, also known as cis-trans isomerism, occurs when atoms are unable to freely rotate due to a rigid structure, such as that found in compounds with carbon-carbon, carbon-nitrogen, or nitrogen-nitrogen double bonds, where the rigidity is due to the double bond, and cyclic compounds, where the rigidity is due to the ring structure.
The geometric isomerism is thus caused by the double bond between the two carbon atoms. Geometrical isomers are chemical isomers that differ in the spatial arrangement of groups or atoms but do not display optical activity.
Cis isomer indicates the orientation when the two largest substituents are on the same side of the double bond. When the two substituents with the highest priority are on the same side of the double bond, the orientation is defined as a trans isomer.
References
- K.R palak,2017, Stereochemistry. Pairavi Prakashan.
- Smith M. B. & March J. (2007). March’s advanced organic chemistry : reactions mechanisms and structure (6. ed.). Wiley-Interscience.
- Bahl A. & Bahl B. S. (2006). A textbook of organic chemistry (for b. sc. students) (18th rev. & enlarged ed. 1st multicolour illustrative). S. Chand.
- https://unacademy.com/content/jee/study-material/chemistry/general-organic-chemistry/
- https://www.pw.live/chapter-iupac-and-goc-class-11
- https://www.vedantu.com/jee-main/chemistry-general-organic-chemistry-goc
