Electrophilic addition reactions comparison

Reactions of alkynes with electrophiles are generally similar to those of alkenes. Because the HOMO of alkynes (acetylenes) is also of n type, it is not surprising that there IS a good deal of similarity between alkenes and alkynes in their reactivity toward electrophilic reagents. The fundamental questions about additions to alkynes include the following. How reactive are alkynes in comparison with alkenes What is the stereochemistry of additions to alkynes And what is the regiochemistry of additions to alkynes The important role of halonium ions and mercurinium ions in addition reactions of alkenes raises the question of whether similar species can be involved with alkynes, where the ring would have to include a double bond ... 

One further comparison aromatic aldehydes, such as benzaldehyde, are less reactive in nucleophilic addition reactions than aliphatic aldehydes because the electron-donating resonance effect of the aromatic ring makes the carbonyl group less electrophilic. Comparing electrostatic potential maps of formaldehyde and benzaldehyde, for example, shows that the carbonyl carbon atom is less positive (less blue) in the aromatic aldehyde. 

Addition as a preceding reaction. In comparison with the use of I2, the more reliable results of the two-step electrophilic addition of IC1 in glacial acetic acid with some CC14 (Wijs iodine number for edible oils and fats) according to... 

This supposition is supported by the correlation of the rate constants for product formation from metMb, horseradish peroxidase, Cu, Zn SOD, Mn SOD, and GSH (147). Electrophilic addition of HNO is assumed to be the rate-limiting step in these reactions. In comparison, the addition of HNO to NH2OH is substantially slower under neutral conditions 1 01 M 1 s 1 (148)], which may be a function of amine pK.r... 

Comparison of the free energies of activation for the addition of an electrophile to an alkyne and to an alkene. Because an alkyne is less reactive than an alkene toward electrophilic addition, we know that A6 for the reaction of an alkyne is greater than the AG for the reaction of an alkene. 

Polyphosphazenes with ferrocenyl substituents 35 have also been synthesized via the functionalization of poly-(methylphenylphosphazene) and related polymers by means of a deprotonation-electrophilic addition strategy (e.g., see Equation (10)). This versatile reaction sequence has yielded materials with, for example, degrees of substitution of 45% and 36% for polymers 35 (R = H and Me), respectively. The molecular weights of the polymers were M = Z.O x 10 and 1.5 x 10 for 35 (R = H and Me), respectively (with PDI values of 1.4-2.0). The glass transition temperatures increased in comparison with the unsubstituted polymer (Tg = 37°G) for 35 with values of 92 °C (R = H) and 87 °G (R = Me). 

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