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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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Analytical Chemistry - Calibration

Analytical Chemistry - Calibration Home > Analytical Chemistry > Calibration CALIBRATION What is calibration? Calibrated instruments|Analytical Chemistry Calibrating a pH meter using buffers Quantitative Analysis by Atomic Absorption Performance Verification of Analytical Balances according to ISO/IEC 17025 Calibration and Outliers - Statistical Analysis Calibration of an instrument in Analytical Chemistry is the operation that determines the functional relationship between measured values (signal intensities S at certain signal positions zi) and analytical quantities characterizing types of analytes qi and their amount ( content , concentration ) n. Calibration includes the selection of the model (its functional form), the estimation of the model parameters as well as the errors, and their validation. During calibration , the in...
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Calibration and Outliers - Statistical Analysis

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The issues an analyst needs to consider when a calibration is performed are as follows: The number of calibration standards – For an initial assessment of the calibration function at least seven different concentrations (including a blank) should be prepared. A calibration standard is a solution prepared from a substance or reference material used to calibrate an instrument.   The concentration of each of the calibration standards - The standard concentrations should cover, at least, the range of concentrations encountered during the analysis of test samples and be evenly spaced across the range. The number of replicates at each concentration   -   At least duplicate measurements at each concentration level. The preparation of the calibration standards -   Calibration solutions are prepared from a pure substance with a known purity value or a solution of a substance with a known concentration. The uncertainty associated with the concentration of the...
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