Exercises: Main organic reactions

Propene ($\mathrm{CH_3-CH=CH_2}$) undergoes an electrophilic addition reaction when treated with water in the presence of dilute sulfuric acid as catalyst, following Markovnikov's rule (the proton is added preferentially to the carbon with the greater number of hydrogens).

1. a) Write the formula and name of the starting reagent and of the major organic product obtained in this hydration.
2. b) Justify, with reasoning, why propan-1-ol is not obtained as the major product.

Complete combustion of alcohols produces carbon dioxide and water vapour, releasing a considerable amount of heat energy.

1. a) Write and balance, using whole-number stoichiometric coefficients, the chemical equation for the complete combustion of ethanol ($\mathrm{CH_3-CH_2OH}$).
2. b) Calculate the volume of carbon dioxide, measured at $25\,^{\circ}\text{C}$ and $1.0\,\text{atm}$, released when $23.0\,\text{g}$ of ethanol is burned completely. Data: relative atomic masses: $\mathrm{C}=12.0$; $\mathrm{H}=1.0$; $\mathrm{O}=16.0$; gas constant $R = 0.082\,\text{atm}\times\text{L}\times\text{mol}^{-1}\times\text{K}^{-1}$.

Alkyl halides can undergo selective transformations depending on the nature of the reagent and the solvent used.

1. a) Write the balanced equation for the nucleophilic substitution reaction between 1-bromopropane ($\mathrm{CH_3-CH_2-CH_2Br}$) and a dilute aqueous solution of sodium hydroxide at moderate temperature, naming the organic product formed.
2. b) State the semi-structural formula and the name of the product that would be obtained if the propene formed in a side reaction were subjected to catalytic hydrogenation with $\mathrm{H_2}$ in the presence of nickel.

The chemical behaviour of a primary alcohol towards a strong oxidising agent such as potassium dichromate in acidic medium depends on the experimental conditions used. Observe the following transformation scheme

1. a) Identify, with justification, the semi-structural formulae and systematic names of the organic products $\mathrm{A}$ and $\mathrm{B}$.
2. b) Justify why immediate distillation of the mixture allows compound $\mathrm{A}$ to be isolated selectively, whereas prolonged reflux with excess oxidant leads to $\mathrm{B}$.

It is desired to synthesise propanone in the laboratory by a two-step sequence starting from propene. In step 1, propene is hydrated in the presence of aqueous sulfuric acid following Markovnikov's rule, giving a secondary alcohol as the major product. In step 2, this alcohol is purified and oxidised with potassium dichromate in acidic medium to obtain propanone.

1. a) Write the equations for both steps, classifying each reaction, with justification, according to the type of organic process (addition, substitution, elimination, oxidation-reduction).
2. b) If you start with $84.0\,\text{g}$ of propene and step 1 has a yield of $75.0\,\%$ while step 2 has a yield of $80.0\,\%$, calculate the final mass of pure propanone obtained. Atomic masses: $\mathrm{C}=12.0$; $\mathrm{H}=1.0$; $\mathrm{O}=16.0$.

A historical organic analysis report describes four unlabelled bottles ($\mathrm{A}$, $\mathrm{B}$, $\mathrm{C}$ and $\mathrm{D}$), each of which contains one of the following pure liquid substances: propanal, propanone, propanoic acid and hex-1-ene. To identify them, three independent chemical tests were recorded, which are analysed as data without reproducing them:

1. Addition of a reddish solution of bromine in carbon tetrachloride: only substance $\mathrm{C}$ decolourises the solution quickly and immediately without evolution of gas.

2. Addition of saturated aqueous sodium hydrogencarbonate solution ($\mathrm{NaHCO_3}$): only substance $\mathrm{D}$ produces clearly visible effervescence.

3. Test with Tollens' reagent (ammoniacal solution of $\mathrm{Ag^+}$): substance $\mathrm{A}$ forms a silver mirror of metallic silver on the walls of the tube when gently heated, whereas $\mathrm{B}$ produces no visible change.

1. a) Assign, with justification, each substance to the letters $\mathrm{A}$, $\mathrm{B}$, $\mathrm{C}$ and $\mathrm{D}$.
2. b) Write the chemical equations corresponding to the positive tests described for $\mathrm{C}$ and $\mathrm{D}$.