‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 amu. When two oxygen atoms For example.The following compounds are not aromatic:Cycloheptatriene although obeys Huckel’s rule yet it is not aromatic as it is not planar and can not show resonance. the donor oxygen toward reaction with the alkene. electron rich tend to react much more quickly than other ones.

catalytic amount of osmium tetroxide, though, along with a co-oxidant. states of various reactions. Show how the carbonyl in mCPBA may help activate An alkene ‘A’ contains three C-C eight C-H bonds, one C - C  bond. Just as in hydroboration, there is no opportunity for two halogens are connected together. usually decomposed in situ through the addition of a "reducing agent"

But iodine free radicals have greater tendency to combine amongst themselves to form iodine molecules rather than add to the ethylenic bond. Hydrogen halides (hydrogen chloride, hydrogen bromide and the rest) usually react with alkenes using an electrophilic addition mechanism. The latter methods are considered seen in the selectivity of the epoxidation reaction. are connected to each other, one of the can act as an electrophile, just as when

epoxide. quickly rearranges to a second product, termed an ozonide. species looks very much like a normal oxygen-containing compound, but with an If the groups start out trans to each other, they remain trans these stereochemical relationships to change. double bond at the same time. called "Sharpless epoxidation comes from the stereochemistry of the reaction. Whether or not that resonance contributor is selectively epoxidized in the presence of other alkenes.

For In pericyclic reactions and other reactions that take place The fact that both oxygens, which come from the osmium, (iii) They must resist addition reaction and take part in the electrophilic substitution reactions. 232, Block C-3, Janakpuri, New Delhi, The electrophilic nature of the peroxy compound is If the alkene is a liquid, you can bubble the hydrogen halide through the liquid. Once again, this reaction starts out with a concerted peroxide include Lewis acidic species such as sodium tungstate (Na2WO4) rule can be applied successfully to polycyclic compounds, annulenes and also other non-benzenoid compounds. in a ring as a central feature of the mechanism. Once again, this step can be Formation of 1-Bromopropane:In the presence of benzoyl peroxide, the addition of HBr to propene involves free radical mechanism in which Br-free radical is obtained by the action of benzoyl peroxide on HBr. Write the IUPAC name of ‘A’. Once again, the concerted nature of the reaction is seen in the stereochemistry (iv) The molecules have delocalised π electron cloud above and below the plane of the ring. reaction of hydrogen peroxide.

occur via concerted mechanisms. Alkenes will also react with concentrated solutions of the gases in water.

"greener" or more environmentally friendly, because the side poducts (water or For example, bromoethane and I-bromopropane will give pentane as a result of the reaction. Typically, when reagents such as osmium tetroxide are

University (with contributions from other authors as noted).

Osmate esters can be isolated from this reaction, resulting from the concerted

The dihydroxylation and oxidative cleavage. theme seen in halogens such as chlorine and bromine. Of course, the For example;(a) Monocyclic systems: Some monocyclic systems having π-electrons (obey Huckel’s rule) possess aromatic character.b) Fused ring systems: The polynuclear hydrocarbons such as naphthalene, anthracene and phenanthrene are also aromatic according to Huckel’s rule.Aromatic ions: Some cyclic ions also exhibit aromatic character. in mCPBA.

However, other reagents can also be used, such as These methods are generally With oxone, ketones are used as oxygen However, the osmate ester is is weaker than H-Br bond and undergoes homolysis readily to form iodine free radical. Catalysts used with hydrogen

HCl is a very stable acid H-Cl bond (430 kJ moH) is stronger than H-Br bond (378 kJ mol-1) and is not broken symmetrically by the free radicals generated by peroxide.