CARBOCATIONS FOR CSIR NET/GATE/IITJAM/IT JEE/NEET

A carbocation is an ion with a positively-charged carbon atom. Among the simplest examples are methenium CH3+, methanium CH5+, and ethanium C2H7+. Some carbocations may have two or more positive charges, on the same carbon atom or on different atoms; such as the ethylene di-cation C2H42+. In present-day chemistry, a carbocation is any positively charged carbon atom, classified in two main categories according to the valence of the charged carbon: +3 in carbenium ions that is protonated carbenes, +5 or +6 in the carbonium ions. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability. Therefore, carbocations are often reactive, seeking to fill the octet of valence electrons as well as regain a neutral charge. One could reasonably assume a carbocation to have sp3 hybridization with an empty sp3 orbital giving positive charge. However, the reactivity of a carbocation more closely resembles sp2 hybridization with a trigonal planar molecular geometry. Non-classical ions Some carbocations such as the norbornyl cation exhibit more or less symmetrical three centre bonding. Cations of this sort have been referred to as non-classical ions. The energy difference between "classical" carbocations and "non-classical" isomers is often very small, and in general there is little, if any, activation energy involved in the transition between "classical" and "non-classical" structures. In essence, the "non-classical" form of the 2-butyl carbocation is 2-butene with a proton directly above the centre of what would be the carbon-carbon double bond. "Non-classical" carbocations were once the subject of great controversy. There are several factors(aromaticity and all positive electronic effects which affects the stability of carbocations. To decide the stability of carbocations, the following concepts can be applied in the given order Aromaticity, Resonance, Mesomeric effect, Hyperconjugation, Inductive effect. #NONCLASSICALCARBOCATIONS #STABILITY #CLASSICALCARBOCATIONS USEFUL LINKS FOUNDATION OF ORGANIC CHEMISTRY :    • Foundation of Organic Chemistry   INDUCTIVE EFFECT:    • Inductive Effect and its Applications/Clas...   HYPERCONJUGATION:    • Hyperconjugation and its Applications/Clas...   RESONANCE:    • Resonance and its Applications/Class XI/B....   AROMATICITY:    • Part 3: Aromaticity (Practice Problems) fo...