Search results
Results from the WOW.Com Content Network
Hyperconjugation can be used to rationalize a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability.
For example, the relative rates of epoxidation increase upon methyl substitution of the alkene (the methyl groups increase the electron density of the double bond by hyperconjugation): ethylene (1, no methyl groups), propene (24, one methyl group), cis-2-butene (500, two methyl groups), 2-methyl-2-butene (6500, three methyl groups), 2,3 ...
The oxidation products derived from methyl are hydroxymethyl group −CH 2 OH, formyl group −CHO, and carboxyl group −COOH. For example, permanganate often converts a methyl group to a carboxyl (−COOH) group, e.g. the conversion of toluene to benzoic acid. Ultimately oxidation of methyl groups gives protons and carbon dioxide, as seen in ...
Alkyl groups are electron donating by inductive effect, and increase the electron density on the sigma bond of the alkene. Also, alkyl groups are sterically large, and are most stable when they are far away from each other. In an alkane, the maximum separation is that of the tetrahedral bond angle, 109.5°. In an alkene, the bond angle ...
The carbon-silicon bond is highly electron-releasing and can stabilize a positive charge in the β position through hyperconjugation.Electrophilic additions to allyl- and vinylsilanes take advantage of this, and site selectivity generally reflects this property—electrophiles become bound to the carbon γ to the silyl group.
[10] [11] This places the σ C–C orbital of the methyl group parallel with the σ* C–O orbital of the activated alcohol. Before the activated alcohol leaves as H 2 O the methyl bonding orbital donates into the C–O antibonding orbital, weakening both bonds. This hyperconjugation facilitates the 1,2-methyl shift that occurs to remove water.
The observed order in this particular reaction however was methyl > ethyl> isopropyl > tert-butyl. In 1935 Baker and Nathan explained the observed difference in terms of a conjugation effect and in later years after the advent of hyperconjugation (1939) as its predecessor.
The +M effect, also known as the positive mesomeric effect, occurs when the substituent is an electron donating group. The group must have one of two things: a lone pair of electrons, or a negative charge. In the +M effect, the pi electrons are transferred from the group towards the conjugate system, increasing the density of the system.