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Carbocations: Factors affecting their Stability

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A carbocation is a species where a carbon atom bonds to three carbon atoms and has a positive charge. Carbocations are electron deficient species and therefore very reactive and unstable . Anything which donates electron density to the electron-deficient center will help to stabilize them. Factors that stabilize them are the following:  Neighboring carbon atoms (inductive effect) Neighboring carbon-carbon multiple bonds (resonance effect) Neighboring atoms with lone pairs (resonance effect) How carbocations are stabilized by neighboring carbons atoms? The stability of carbocations decreases as the number of carbons attached to the C+ decreases. That means that tertiary carbocations are more stable than secondary that in turn are more stable than primary (Fig. 1). Fig. 1: Carbocation stability increases as methyl substitution increases around the electron deficient carbon C+. The methyl groups (-CH 3 ) are electron donating and therefore stabilize the positive charge (inductive ...
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Quantitative Analysis by Atomic Absorption

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Quantitative Analysis by Atomic Absorption Home > Analytical Chemistry > Analytical Chemistry - Atomic Absorption > Atomic Absorption Spectrometry (AAS) > Light Sources for Atomic Absorption > Quantitative Analysis by Atomic Absorption   Quantitative Analysis by Atomic Absorption   The capability of an atom to absorb very specific wavelengths of light is utilized in atomic absorption spectrometry . Light of a specific wavelength and of initial intensity I o is focused on the flame cell containing ground state atoms. The initial light intensity is decreased by an amount determined by the atom concentration in the flame cell. The light is then directed to the detector where the reduced intensity, I t , is measured. The amount of light absorbed is determined by comparing I t   to I o and according to Beer’s law :   A = log I o / I t = α * c * d         (1)   Abso...
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Troubleshooting HPLC / Liquid Chromatography Systems – Peak Tailing

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In a previous post entitled  " TroubleshootingLC / HPLC Systems – Tailing Peaks " peak tailing due to bad columns and sample overload was explained and methods were proposed to fix it.  Peaks with strange shapes represent one of the most common problems that can arise in the LC/HPLC laboratory.  It should be first explained why tailing is bad : Peaks with tailing can be hard to integrate The precision and the reliability of assay methods involving distorted – peaks with tailing – is often poor when compared to good chromatography Resolution is low when peaks show tailing  Another cause of peak tailing is when wrong solvent is used to dissolve the sample. Wrong Solvent for Sample Peak tailing is observed when the volume and the kind of solvent used to dissolve the sample is not appropriate. Ideally a small volume of sample (dissolved in the mobile phase) should be injected. However, when a relatively large volume of a solvent stronger than the mobile phase is injec...
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