Polar addition oxygen

Overall the reaction is classified as an addition Water adds to the carbonyl group Hydrogen becomes bonded to the negatively polarized carbonyl oxygen hydroxyl to the positively polarized carbon... 

The H-O bond is weakened or increasingly polarized by the additional oxygen atoms that are bonded to the central chlorine atom in HCIO3. 

A wide variety of photoadditions to unsaturated oxygen and sulfur heterocycles has been reported. It has, however, proved difficult to classify these processes, especially as the reaction mechanisms are not fully understood in all cases. Most additions of solvent to oxygen heterocycles arise via hydrogen abstraction pathwyas, often initiated by added ketone. Polar addition is relatively rare in these compounds the addition of methanol to... 

On the C=C double bond, 2+2 cycloaddition occurs with conjugated olefins (Scheme 4.6), e.g., with the antidepressant protriptyline (Gasparro and Kochevar, 1982) and in particular with a,P-unsaturated ketones (e.g., with menadione (8), which yields the. vyn-cyclobutane dimer in the solid state and the anti-isomer by irradiation in acetone solution (Scheme 4.7 (Marciniec and Witkowska, 1988). The epoxide is obtained in the presence of oxygen (Jones and Sharpies, 1984) (see later in this chapter for other oxidations). Polar addition to arylalkenes has also been observed,... 

Learning Goal The principal reaction of the carbonyl group is the addition reaction across the polar carbon-oxygen bond. Such reactions require that a catalytic amount of acid be present in solution, as shown by the H+ over the arrow for the reactions shown in the following examples. 

Irradiation of phenyl substituted diacetylenes yields both protonated products and reduction products. The photoreduction products seem to originate from the triplet excited state, since oxygen quenches the photoreduction almost completely. However, oxygen does not quench the polar addition reaction, supporting a singlet excited state mechanism for the formation of type B photoproducts (Cl protonation product). 

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