3 63 heats of hydrogenation heats of hydrogenation

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Unformatted text preview: of Hydrogenation Heats of Hydrogenation and Stability Since more substituted alkenes are more stable the heat of hydrogenation of substituted alkenes should be lower. Heats of Hydrogenation and Stability Heats less stable more stable Heats of Hydrogenation and Stability Heats 6.4 Electrophilic Addition of Hydrogen Halides to Alkenes Alkenes Addition of Hydrogen Halides to Alkenes Addition of H-X to an alkene yields an alkyl halide according to the equation: Addition of Hydrogen Halides to Alkenes The π-bond of the alkene which is electron rich (red in the electrostatic potential map) reacts with the polarized partially positive hydrogen (purple) of the HX. Addition of Hydrogen Halides to Alkenes More substituted double bonds are more electron rich so they react faster. HI is the strongest acid so it reacts fastest in the series. Selectivity of Addition of HX to Alkenes Addition of HX is highly selective: Markovnikov’s Rule for Addition of HX Markovnikov’s rule: when an unsymmetrically substituted alkene reacts with a hydrogen halide, the hydrogen adds to the carbon that has the more hydrogens, and the halogen adds to the carbon that has fewer hydrogens. Mechanism of A...
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