Organic Chemistry

Syn Dihydroxylation of Alkenes – Converting an alkene to a glycol requires adding a hydroxyl group to each end of the double bond. This addition is called Dihydroxylation of Alkenes or dihydroxylation (or hydroxylation) of the double bond. – We have seen that epoxidation of an alkene, followed by acidic …

Epoxidation of Alkenes – Some of the most important reactions of alkenes involve oxidation. – When we speak of oxidation, we usually mean reactions that form carbon–oxygen bonds. (Halogens are oxidizing agents, and the addition of a halogen molecule across a double bond is formally an oxidation as well.) – …

Addition of Carbenes to Alkenes – Methylene (:CH2) is the simplest of the carbenes: uncharged, reactive intermediates that have a carbon atom with two bonds and two nonbonding electrons. – Like borane (BH3), methylene is a potent electrophile because it has an unfilled octet. – It adds to the electronrich …

Catalytic Hydrogenation of Alkenes – Although we have mentioned catalytic hydrogenation before, we now consider the mechanism and stereochemistry in more detail. – Hydrogenation of an alkene is formally a reduction, with H2 adding across the double bond to give an alkane. – The process usually requires a catalyst containing …

Formation of Halohydrin – A halohydrin is an alcohol with a halogen on the adjacent carbon atom. – In the presence of water, halogens add to alkenes to form halohydrins. – The electrophilic halogen adds to the alkene to give a halonium ion, which is also electrophilic. – Water acts …

Addition of Halogens to Alkenes – Addition of Halogens to Alkenes gives vicinal dihalides. (A) Mechanism of Halogen Addition – A halogen molecule (Br2, Cl2, or I2) is electrophilic; a nucleophile can react with a halogen, displacing a halide ion: – In this example, the nucleophile attacks the electrophilic nucleus …

Hydroboration of Alkenes – We have seen two methods for hydrating an alkene with Markovnikov orientation. – What if we need to convert an alkene to the anti-Markovnikov alcohol? – For example, the following transformation cannot be accomplished using the hydration procedures covered thus far. – Such an anti-Markovnikov hydration …

– Oxymercuration–demercuration of alkenes is another method for converting alkenes to alcohols with Markovnikov orientation. Hydration of alkenes by Oxymercuration–Demercuration – Many alkenes do not easily undergo hydration in aqueous acid. – Some alkenes are nearly insoluble in aqueous acid, and others undergo side reactions such as rearrangement, polymerization, or …

Hydration of Alkenes will be discussed by Addition of Water Addition of Water: Hydration of Alkenes – An alkene may react with water in the presence of a strongly acidic catalyst to form an alcohol. – Formally, this reaction is a hydration (the addition of water), with a hydrogen atom …

Alkyl halides as Solvents – Alkyl halides are used primarily as industrial and household solvents. – Carbon tetrachloride (CCl4) was once used for dry cleaning, spot removing, and other domestic cleaning. – Carbon tetrachloride is toxic and carcinogenic (causes cancer), however, so dry cleaners now use 1,1,1-trichloroethane and other solvents …

Addition of Hydrogen Halides to Alkenes : Markovnikov’s Rule Orientation of Addition: Markovnikov’s Rule – The simple mechanism shown for addition of HBr to but-2-ene applies to a large number of electrophilic additions. – We can use this mechanism to predict the outcome of some fairly complicated reactions. – For …

Electrophilic Addition to Alkenes Reactivity of the Carbon–Carbon Double Bond – All alkenes have a common feature: a carbon–carbon double bond. – The reactions of alkenes arise from the reactivity of the carbon–carbon double bond. – Once again, the concept of the functional group helps to organize and simplify the …

Methods for Synthesis of Alkenes – Six methods for Synthesis of Alkenes will be discussed as follow: (1) Dehydrohalogenation of alkyl halides – Dehydrohalogenation is the elimination of a hydrogen and a halogen from an alkyl halide to form an alkene. – dehydrohalogenation can take place by the E1 and …

Alkene Synthesis by High-Temperature Industrial Methods (1) Catalytic Cracking of Alkanes – The least expensive way to make alkenes on a large scale is by the catalytic cracking of petroleum: heating a mixture of alkanes in the presence of a catalyst (usually aluminosilicates). – Alkenes are formed by bond cleavage …

Alkene Synthesis by Dehydration of Alcohols – Dehydration of alcohols is a common method for making alkenes. The word dehydration literally means “removal of water.” – Dehydration is reversible, and in most cases the equilibrium constant is not large. – In fact, the reverse reaction (hydration) is a method for …

Alkene Synthesis by Elimination of Alkyl Halides – Dehydrohalogenation is the elimination of a hydrogen and a halogen from an alkyl halide to form an alkene. – dehydrohalogenation can take place by the E1 and E2 mechanisms. – The second-order elimination (E2) is usually better for synthetic purposes because the …

Physical Properties of Alkenes (1) Boiling Points and Densities – Most physical properties of alkenes are similar to those of the corresponding alkanes. – For example, the boiling points of but-1-ene, cis-but-2-ene, trans-but-2-ene, and n-butane are all close to 0 °C. – Also like the alkanes, alkenes have densities around …

Stability of Alkenes – In making alkenes, we often find that the major product is the most stable alkene. – Many reactions also provide opportunities for double bonds to rearrange to more stable isomers. – Therefore, we need to know how the stability of an alkene depends on its structure. …

Commercial Importance of Alkenes – Because the carbon–carbon double bond is readily converted to other functional groups, alkenes are important intermediates in the synthesis of polymers, drugs, pesticides, and other valuable chemicals. – Ethylene is the organic compound produced in the largest volume, at around 160 billion pounds per year …

Nomenclature of Alkenes – Simple alkenes are named much like alkanes, using the root name of the longest chain containing the double bond. The ending is changed from -ane to -ene. – For example, (ethane) becomes “ethene,” (propane) becomes “propene,” and “cyclohexane” becomes “cyclohexene”. – When the chain contains more …