What is Carbon Bonding?
It is basically an association between two C that is formed by sharing a pair of electrons among them. Commonly, this is a single or sigma (σ) bond. Sometimes double or triple or pi (Π) bonds can also be formed. These are formed when orbitals of two C atoms get hybridized.
Covalency in Carbon Atoms
Mutual sharing of electrons resulting in the formation of a force of attraction is defined as a covalent bond between two atoms. The combining partners may share one, two, or three pairs of negatively charged particles. Ions do not have any existence in the covalent compounds but molecules do exist. Their melting and boiling points are generally low. The number of negatively charged particles shared by an atom during the formation of covalent bonds is known as the covalency of that element. Covalency depends on a shared pair of negatively charged particles. Sharing one pair forms monovalency, sharing two pairs’ forms bivalency, and so on.
Tetravalency in Carbon Atoms
The atomic number of C is six. The first two shells have six electrons. In the excited state, carbon seems to be a bivalent one. But in actuality, it displays tetravalency in the combined state. In the ground state, they have two negatively charged particles in their outer orbit, but in an excited state, they have four that can take part in forming covalency. Therefore, carbon is tetravalent in nature. It can gain four negatively charged particles to form C4- anion or lose four to form a C4+ cation. Both of these would be a problem for carbon to achieve stability by the octet rule. To overcome this problem carbon makes bonding by sharing its outermost particles. This results in the formation of the system covalently bonded to one to 4 numbers of C or other elements or groups.
Hybridization in Molecules
This is the mixing of atomic orbitals to form a set of new equivalent orbitals. It can be produced by head-on overlapping or side-on overlapping. It is termed hybridization. Generally, C complexes have three types of hybridization.
It is involved in saturated organic moieties containing single σ associations. In this case, one’s orbital and 3 p orbitals are used while forming the attachment by head-on overlapping. The bond angle is 109°28′ and the geometry is tetrahedral. They have 25% s-character. Examples include methane (CH4), CCl4, etc.
It is involved in organic moieties having C linked by double-bonded Π association. Here one s and two p orbitals are hybridized. The Angle is 120° and the geometry is trigonal planar. They have 33.33% s-character. Examples include Ethylene (CH2=CH2).
They are involved in organic moieties having C linked by a triple bonded Π association. One s and one p orbitals are hybridized by side-on overlapping. The angle becomes 180° and the geometry is linear. They have 50% s-character and for this reason, sp hybridized C has a high value to electronegativity. Examples include Acetylene (CHΞCH).
Size of the Hybrid Orbitals
The size of the hybrid orbitals follows the order sp3>sp2>sp.
Electronegativity of different orbitals
- Electronegativity ∝ percentage of s-character.
- Electronegativities of different hybrid and nonhybrid orbitals in decreasing order are as follows: s>sp>sp2>sp3>p.
- Due to high electronegativity, H linked with sp hybridized C is acidic in nature.
Length and strength of association
- C-C length increases with a decrease in the percentage of s-character.
- Shorter is the length, greater is the compression between atomic nuclei, and hence greater is the strength of the association.
Catenation of Carbon atoms
The ability of an atom of a system to link with each other to form chains of identical groups is termed catenation. C exhibits catenation most due to strong C-C attachment. Its tetravalency helps in this occurrence also.
The Formation of Multiple Bonds between C and C
Because of the smaller size of the C, it can form more than one bond (double and triple) with any group, not the carbon atom only but with others such as oxygen, nitrogen. The making of such kinds of structures can increase a variety of C compounds. They can be either organic or inorganic compounds. C tends to form a large group of organic compounds. It is the backbone of organic compounds. The best-known example includes hydrocarbons. They are organic molecules formed from C and H2. They are Methane (CH4), Ethane (C2H6), Ethylene (C2H4), Acetylene (C2H2), Chloroform (CHCl3), CCl4, Cyanides (CN-), etc. Inorganic molecules include CO2, Carbonic acid (H2CO3), CO, etc.
Saturated and Unsaturated Molecules containing Carbon Atoms
Organic molecules containing C can be classified as saturated or unsaturated depending upon whether they form single or multiple covalent bonds.
Molecular structures made up of C and H whose linked carbon atoms have one C-C attachment only are referred to as saturated hydrocarbons. In this case, the C-H associations are like single covalent bonds. They are called so due to the complete utilization of the tetravalency of the carbon atom and any hydrogen or other groups cannot attach to it. Thus, they can participate in the substitution reactions only. They are also representative of open-chain aliphatic organic molecules. They are known as alkanes like Methane (CH4), Ethane(C2H6), Propane (C3H8), Butane (C4H10), etc.
Compounds of C and H that contain one double or triple covalent bond between carbon atoms (C=C or C≡C) are referred to as unsaturated hydrocarbons. In this case, all the valences exhibited by the carbon atoms are not used completely by hydrogens, or other groups can attach to them. Thus, they can participate in the addition reactions (add-on hydrogens) as they exhibit more numbers of hydrogens that are lesser than the saturated ones. They are known as alkenes (C=C) or alkynes (C≡C) such as Ethylene (C2H4), Propylene (C3H6), Acetylene (C2H2), Methyl acetylene (C3H4), etc.
The unique property of the C-C bond has also led to the making of compounds that can exhibit the same formula of the molecules but have differences in the structures. This occurrence of the formation of the different structures with the same molecular formulas that gives rise to different characteristics is called isomerism. These substances with the same molecular formulas are termed isomers of each other. Isomerism which arises due to different branching of the carbon atoms is called chain isomerism. Butane (C4H10) has two isomers, one is n-butane with a linear 4-C series, and another is isobutane with branching at C-2. Another example is pentane which has 3 isomers, n-pentane with linear 5-C series, isopentane with linear 4-C series and branching at C-2 with a methyl group, neopentane with linear 3-C series, and branching at C-2 with two methyl groups.
Synthesis of C-C attachments in Organic Chemistry
Various synthetic reactions are there which can form a new C-C association from two different articles. Some of them are as follows.
This involves the treatment of 1,3-butadiene or any other conjugated dienes with an alkene or an alkyne. No catalyst is needed. The alkenes or alkynes used in this reaction are dienophiles or diene lovers. The net result is the formation of two new σ attachments and one new π association at the expense of 3 original Π associations.
CH2=CH=CH=CH2 + CH2=CH2 → Cyclohexene (adduct)
Aldol Condensation Reaction
The enolizable C substances (containing Alpha-H) in the presence of H+ or OH- (at or below room temperature) undergo dimerization, producing aldol. This can produce a new C-C association between two carbonyls. The following dehydration gives α,β-unsaturated aldehydes, or ketones. The reaction involves the nucleophilic addition of an enolate ion to the carbonyl group.
By this reaction, alkanes are produced by condensing alkyl halides with sodium metal in a dry ether medium. Here a new C-C σ-attachment is formed between C of two alkyl halides. Only symmetrical alkanes can be produced by this method.
R-Br + 2Na + Br-R → 2NaBr + R-R
CH3-Cl + 2Na + Cl-CH3 → 2NaCl + CH3-CH3
- Most of the time, students forget to put H atoms attached to the C atom.
- The valency of the C atoms is mistakenly put.
% amount of C in an analyte = (12 X mass of produced CO2 X 100) / (44 X mass of the analyte)
Context and Applications
This topic is significant in the professional exams for both undergraduate and postgraduate courses, especially for
- B.Sc. in Chemistry
- M.Sc. in Chemistry
- B.Sc. in Biochemistry
- M.Sc. in Biochemistry
- Half-life of C
- Allotropy of C
- Electrovalent association
- Homologous series
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