(a)(i) What is a functional group?
(ii) State the functional group in each of the following compounds: I. CH\(_3\)CH\(_2\)CH(CH\(_3\))OH; II. CH\(_3\)CH\(_2\)CH\(_2\)COOH.
(b)(i) Complete the following equations:
(ii) Draw the structure(s) of the product(s) formed in (b)(i) above.
(c)(i).Write an equation for the prepzration of butan-2-ol from butene.
(d) (i) Give the reagents required for the following conversions to take place: I. CH\(_2\) = CH\(_2\) to CH\(_3\)CH\(_2\)OH; II. CH\(_3\)CH\(_2\)OH to CH\(_3\)COOH; Ill. CH\(_3\)COOH to CH\(_3\)COOCH\(_2\)CH\(_3\).
(e) Consider the following organic structure; CH\(_3\)OHCHCH = CHCOOH
(i) State what would be observed when the organic compound is treated with each of the following reagents: I. cold NaHCO\(_{3(aq)}\); II. hot solution of I\(_2\) in NaOH\(_{(aq)}\); Ill. bromine water.
(a)(i) Functional group. A functional group is an atom or a group of atoms present in a molecule that is responsible for the characteristic chemical properties (reactions) of that molecule. Compounds having the same functional group belong to the same homologous series.
(a)(ii) Functional group in each compound.
- I. \(CH_3CH_2CH(CH_3)OH\) (butan-2-ol): the hydroxyl group, \(-OH\) (alcohol).
- II. \(CH_3CH_2CH_2COOH\) (butanoic acid): the carboxyl group, \(-COOH\) (carboxylic acid).
(b)(i) Completed equations.
I. Acid hydrolysis of propyl ethanoate. The ester is split by water; the acid catalyst regenerates the parent acid and alcohol:
\[CH_3COOCH_2CH_2CH_3 + H_2O \xrightarrow{\;H^{+},\;\text{heat}\;} CH_3COOH + CH_3CH_2CH_2OH\]
Products: ethanoic acid and propan-1-ol.
II. Base (alkaline) hydrolysis of methyl pentanoate (saponification). With \(NaOH\) the carboxylic acid is obtained as its sodium salt:
\[CH_3CH_2CH_2CH_2COOCH_3 + NaOH \xrightarrow{\;\text{heat}\;} CH_3CH_2CH_2CH_2COONa + CH_3OH\]
Products: sodium pentanoate and methanol.
(b)(ii) Structures of the products.
From I:
- Ethanoic acid:
O
||
CH3 - C - O - H
- Propan-1-ol: \(CH_3-CH_2-CH_2-OH\)
From II:
(c)(i) Preparation of butan-2-ol from butene. By acid-catalysed hydration of but-1-ene. Water adds across the double bond, and by Markovnikov addition the \(-OH\) attaches to the more substituted carbon, giving the secondary alcohol butan-2-ol:
\[CH_3CH_2CH=CH_2 + H_2O \xrightarrow{\;H^{+}\;(\text{conc. } H_2SO_4)\;} CH_3CH_2CH(OH)CH_3\]
(d)(i) Reagents required.
- I. \(CH_2=CH_2 \rightarrow CH_3CH_2OH\): steam (water) with concentrated \(H_2SO_4\) (or \(H_3PO_4\)) as catalyst, i.e. acid-catalysed hydration.
- II. \(CH_3CH_2OH \rightarrow CH_3COOH\): an oxidising agent, acidified potassium dichromate(VI), \(K_2Cr_2O_7/H_2SO_4\) (or acidified \(KMnO_4\)), heated under reflux.
- III. \(CH_3COOH \rightarrow CH_3COOCH_2CH_3\): ethanol, \(CH_3CH_2OH\), with concentrated \(H_2SO_4\) as catalyst (esterification).
(e)(i) Observations with the compound \(CH_3CH(OH)CH=CHCOOH\). This molecule contains three reactive centres: a carboxyl group \(-COOH\), a methyl-carbinol group \(CH_3CH(OH)-\), and a carbon-carbon double bond \(C=C\).
- I. Cold \(NaHCO_{3(aq)}\): brisk effervescence occurs; a colourless, odourless gas (carbon dioxide) is evolved which turns limewater milky. This confirms the acidic \(-COOH\) group. \[-COOH + NaHCO_3 \rightarrow -COONa + H_2O + CO_2\uparrow\]
- II. Hot \(I_2\) in \(NaOH_{(aq)}\): a yellow precipitate of triiodomethane (iodoform, \(CHI_3\)) with a characteristic antiseptic smell is formed. This is the positive iodoform test given by the \(CH_3CH(OH)-\) (methyl-carbinol) group.
- III. Bromine water: the reddish-brown bromine water is decolourised (turns colourless). The \(C=C\) double bond undergoes an addition reaction with bromine.
(a)(i) Functional group. A functional group is an atom or a group of atoms present in a molecule that is responsible for the characteristic chemical properties (reactions) of that molecule. Compounds having the same functional group belong to the same homologous series.
(a)(ii) Functional group in each compound.
- I. \(CH_3CH_2CH(CH_3)OH\) (butan-2-ol): the hydroxyl group, \(-OH\) (alcohol).
- II. \(CH_3CH_2CH_2COOH\) (butanoic acid): the carboxyl group, \(-COOH\) (carboxylic acid).
(b)(i) Completed equations.
I. Acid hydrolysis of propyl ethanoate. The ester is split by water; the acid catalyst regenerates the parent acid and alcohol:
\[CH_3COOCH_2CH_2CH_3 + H_2O \xrightarrow{\;H^{+},\;\text{heat}\;} CH_3COOH + CH_3CH_2CH_2OH\]
Products: ethanoic acid and propan-1-ol.
II. Base (alkaline) hydrolysis of methyl pentanoate (saponification). With \(NaOH\) the carboxylic acid is obtained as its sodium salt:
\[CH_3CH_2CH_2CH_2COOCH_3 + NaOH \xrightarrow{\;\text{heat}\;} CH_3CH_2CH_2CH_2COONa + CH_3OH\]
Products: sodium pentanoate and methanol.
(b)(ii) Structures of the products.
From I:
- Ethanoic acid:
O
||
CH3 - C - O - H
- Propan-1-ol: \(CH_3-CH_2-CH_2-OH\)
From II:
(c)(i) Preparation of butan-2-ol from butene. By acid-catalysed hydration of but-1-ene. Water adds across the double bond, and by Markovnikov addition the \(-OH\) attaches to the more substituted carbon, giving the secondary alcohol butan-2-ol:
\[CH_3CH_2CH=CH_2 + H_2O \xrightarrow{\;H^{+}\;(\text{conc. } H_2SO_4)\;} CH_3CH_2CH(OH)CH_3\]
(d)(i) Reagents required.
- I. \(CH_2=CH_2 \rightarrow CH_3CH_2OH\): steam (water) with concentrated \(H_2SO_4\) (or \(H_3PO_4\)) as catalyst, i.e. acid-catalysed hydration.
- II. \(CH_3CH_2OH \rightarrow CH_3COOH\): an oxidising agent, acidified potassium dichromate(VI), \(K_2Cr_2O_7/H_2SO_4\) (or acidified \(KMnO_4\)), heated under reflux.
- III. \(CH_3COOH \rightarrow CH_3COOCH_2CH_3\): ethanol, \(CH_3CH_2OH\), with concentrated \(H_2SO_4\) as catalyst (esterification).
(e)(i) Observations with the compound \(CH_3CH(OH)CH=CHCOOH\). This molecule contains three reactive centres: a carboxyl group \(-COOH\), a methyl-carbinol group \(CH_3CH(OH)-\), and a carbon-carbon double bond \(C=C\).
- I. Cold \(NaHCO_{3(aq)}\): brisk effervescence occurs; a colourless, odourless gas (carbon dioxide) is evolved which turns limewater milky. This confirms the acidic \(-COOH\) group. \[-COOH + NaHCO_3 \rightarrow -COONa + H_2O + CO_2\uparrow\]
- II. Hot \(I_2\) in \(NaOH_{(aq)}\): a yellow precipitate of triiodomethane (iodoform, \(CHI_3\)) with a characteristic antiseptic smell is formed. This is the positive iodoform test given by the \(CH_3CH(OH)-\) (methyl-carbinol) group.
- III. Bromine water: the reddish-brown bromine water is decolourised (turns colourless). The \(C=C\) double bond undergoes an addition reaction with bromine.
