Assessment Task:
Hydrocarbon Bonding and Isomers - Chemistry Assessment Answer

ACTIVITY 1. Hydrocarbon Bonding and Isomers

1.1. To justify the tetra-valency in acetylene (ethyne), the carbon atom must have 4 atomic orbitals available for bonding. The electronic configuration of carbon in its ground state does not justify why carbon is tetravalent. Show how the ground state valence electron configuration of carbon can form hybrid orbitals that better justify the bonding in ethyne. Your answer must include a labelled drawing of orbitals overlapping to form the bonds of ethyne.

1.2. The following diagram shows the enthalpy of hydrogenation data for cyclohexene, cyclohexadiene, a theoretical triene and benzene.

a) Place the correct structures in the boxes on the below energy profile.

b) Explain why even though benzene has an extra bond to break, it has a lower enthalpy of hydrogenation than cyclohexadiene. Include resonance structures as part of your explanation.

1.3. The following drugs are chiral compounds that can exist as two stereoisomers:

a) For both molecules, identify the carbon that is the stereocentre and assign it as (R) or (S).

b) Discuss the implications this stereocentre has on the biological activity of these compounds.

 

ACTIVITY 2. Reaction of Hydrocarbons

2.1. For the following addition reaction of an alkene:

a) Explain which of the two options shown will give the major product in terms of the stability of the intermediates shown.

b) State the rule that governs the outcome of such addition reactions.

c) Complete the mechanism to show the resulting major product.

2.2. Aromatic compounds will only react with halogens in the presence of a catalyst which generates a reactive electrophile. An example is the bromination of benzene.

a) Complete the catalyst mechanism below by drawing appropriate curved arrows and structures.

b) Complete the following mechanism to show how the aromatic ring undergoes electrophilic substitution including all the resonance contributors for the intermediate carbocation.

2.3. Provide a summary of the different redox reactions that involve alcohols by constructing your own “mud map”. Include reagents and be sure to show any selectivity or limitations as appropriate.

 

ACTIVITY 3. Nucleophilic Substitution and Elimination Reactions

3.1. The following complete mechanism shows an SN1 reaction of alcohol.

a) Draw the structures of any missing intermediates or products.

b) Label each step appropriately as either protonation, deprotonation, loss of leaving group or rearrangement.

c) Draw in any necessary curved arrows to show electron movement in this mechanism.

3.2. Consider the competing elimination and nucleophilic substitution mechanisms that may take place when the following primary haloalkane is reacted with sodium hydrosulfide, a weak base but strong nucleophile.

a) Which mechanisms are most likely, and which are least likely in terms of the substrate and the reagent?

b) Would change the reagent to NaOH, a stronger base, significantly change the outcome of this reaction?

c) Would the same apply if we used the following primary haloalkane and the similar reagent NaOMe that is both a strong base and nucleophile?

 

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  • Uploaded By : Mitchell Lee
  • Posted on : November 11th, 2018

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