Alkenes: Structure and Reactivity

Tamoxifen, a drug used in the treatment of breast cancer, and clomiphene, a drug used in fertility treatment, have similar structures but very different effects. Assign E or Z configuration to the double bonds in both compounds.

Rank the carbocations below in terms of increasing stability:

Use Hammond’s Postulate to determine which alkene in each pair would be expected to form a carbocation faster in an electrophilic addition reaction:

Carbocations can be stabilized by resonance. Draw all the resonance forms that would stabilize each carbocation:

Predict the major product in each of the following reactions:

Predict the major product from addition of HBr to each of the following alkenes:

Allene (1,2-propadiene), H₂C = C = CH₂, has two adjacent double bonds. What kind of hybridization must the central carbon have? Sketch the bonding $\mathrm{\pi }$orbitals in allene. What shape do you predict for allene?

Retin A, or retinoic acid, is a medication commonly used to reduce wrinkles and treat severe acne. How many different isomers arising from double-bond isomerizations are possible?

Vinylcyclopropane reacts with HBr to yield a rearranged alkyl bromide. Follow the flow of electrons as represented by the curved arrows, show the structure of the carbocation intermediate in brackets, and show the structure of the final product.

tert-Butyl [RCO₂C(CH₃)₃] esters are converted into carboxylic acids [RC0₂H] by reaction with trifluoroacetic acid, a reaction useful in protein synthesis (Section 26-7). Assign E, Z designation to the double bonds of both reactant and product in the following scheme, and explain why there is an apparent change in double-bond stereochemistry:

Draw an energy diagram for the addition of HBr to 1-pentene. Let one curve on your diagram show the formation of 1-bromopentane product and another curve on the same diagram show the formation of 2-bromopentane product. Label the positions for all reactants, intermediates, and products. Which curve has the higher-energy carbocation intermediate? Which curve has the higher-energy first transition state?

Sketch the transition-state structures involved in the reaction of HBr with 1-pentene (Problem 7-69). Tell whether each structure resembles reactant or product.

Question: When methyl vinyl ether reacts with a strong acid, the proton adds to

C2 exclusively, instead of C1 or the oxygen atom. Draw the three protonated

forms of methyl vinyl ether and explain this observation

Question: Addition of HCl to 1-isopropylcyclohexene yields a rearranged product.

Propose a mechanism, showing the structures of the intermediates and using curved arrows to indicate electron flow in each step

Question: Calculate the degree of unsaturation in the following formulas, and

draw five possible structures for each:

$$\begin{gathered} {\mathbf{\text{(a) C}}}_{\mathbf{\text{10}}}{\mathbf{\text{H}}}_{\mathbf{\text{16}}} \\ {\mathbf{\text{(b) C}}}_{\mathbf{\text{8}}}{\mathbf{\text{H}}}_{\mathbf{\text{8}}}\mathbf{\text{O }} \\ {\mathbf{\text{(c) C}}}_{\mathbf{\text{7}}}{\mathbf{\text{H}}}_{\mathbf{\text{10}}}{\mathbf{\text{Cl}}}_{\mathbf{\text{2}}} \\ {\mathbf{\text{(d) C}}}_{\mathbf{\text{10}}}{\mathbf{\text{H}}}_{\mathbf{\text{16}}}{\mathbf{\text{O}}}_{\mathbf{\text{2}}} \\ {\mathbf{\text{(e) C}}}_{\mathbf{5}}{\mathbf{\text{H}}}_{\mathbf{9}}{\mathbf{\text{NO}}}_{\mathbf{\text{2}}} \\ {\mathbf{\text{(f)C}}}_{\mathbf{8}}{\mathbf{\text{H}}}_{\mathbf{10}}\mathbf{\text{ClNO }} \end{gathered}$$

How many hydrogens does each of the following compounds have?

(a) ${\text{C}}_{\text{8}}{\text{H}}_{\text{?}}{\text{O}}_{\text{2}}$, has two rings and one double bond

(b)${\text{C}}_{\text{7}}{\text{H}}_{\text{?}}\text{N}$ , has two double bonds

(c)${\text{C}}_9{\text{H}}_{\text{?}}\text{NO}$ , has one ring and three double bonds

Question: Loratadine, marketed as an antiallergy medication under the name Claritin, has four rings, eight double bonds, and the formula C₂₂H_?CIN₂O₂ . How many hydrogens does loratadine have? (Calculate your answer; don’t count hydrogens in the structure.)

Question. Draw and name the six alkene isomers, C₅H₁₀ , including E, Z isomers:

Q 44 Draw and name the 17 alkene isomers,C₆H₁₂ , including E, Z isomers.

Question: Rank the following sets of substituents according to the Cahn–Ingold– Prelog sequence rules: –

Question: Assign E or Z configuration to each of the following compounds:

Question : Which of the following E, Z designations are correct, and which are  incorrect ?

Question : Trans-2-Butene is more stable than cis-2-butene by only 4 kJ/mol, but trans-2,2,5,5-tetramethyl-3-hexene is more stable than its cis isomer by 39 kJ/mol. Explain.