NJC [Tutorial Answer] Introduction to Organic Chemistry

1Introduction to Organic Chemistry TutorialStructure and naming1Give the IUPAC name for each compound.(a)CH3CH(CH3)CH2CH(OH)CH34-methylpentan-2-ol(b)CH2=CHCH=CHBr1-bromobuta-1,3-diene(c)CH3Cl1-chloro-4-methylcyclohexane(d)CH3CH(CO2H)CH2CH32-methylbutanoic acid2Draw the skeletal formula of each compound.(a)2,2,4-trimethylhexane(b)2,4-dibromomethylbenzeneBrBr(c)1-ethyl-3,3-dimethylcyclopentane3For each part, the name given is incorrect. Draw the skeletal formula for each and give its correct IUPAC name.(a)2-ethylpentane3-methylhexane(b)2-chloro-2-ethylbut-3-ene3-chloro -3-methylpent -1-eneCl(c)2,3-diethylcyclopentane1,2-diethylcyclopentane(d)1,1-dimethy-3-propylhexane Hybridisation 4State the type of hybridisation of each carbon in each species.(a)CH3– sp3 (b)CH3CH2OH both sp3(c)CH3CHO sp3 and sp2(d)CH3+ sp2 (e)

C1 to C4 and C7: sp2; C5, C6 and C8: sp3Type of reaction5Classify each reaction as addition, elimination, condensation, oxidation, reduction or substitution.(a)CH3CH3 + Br2  CH2BrCH3 + HBrsubstitution(b)CH2=CHCH3 + Br2  BrCH2CH2BrCH3addition(c)CH3CH2CH2OH + 2[O]  CH3CH2CO2H + H2Ooxidation(d)CH3CO2H + 2[H]  CH3CHO + H2Oreduction(e)Cl COCH2CH3+ +HClOH OCOCH2CH3 condensation(f)+Cl HCl elimination6[N08/I/19]The bond lengths in buta-1,3-diene differ from those which might be expected. The carbon-carbon bond length in ethane is 0.154nm and in ethene is 0.134nm. The central single bond in buta-1,3-diene (C2-C3), however, is shorter than the single bond in ethane: it is 0.147nm. CH2CHCHCH212340.134nm0.134nm0.147nmWhat helps to explain this C2-C3 bond length?AIt is a sp2-sp2 overlap.BIt is a sp2-sp3 overlap.CThe electrons in the filled p orbitals on C2 and C3 repel each other.DThe sp3-sp3 bonding is pulled shorter by a p-p ( bond) overlap.In ethane, the carbons car sp3 hybridised, hence the single bond in ethane is formed from the overlap of sp3 hybrid orbitals; while in buta-1,3-diene, the carbons are sp2 hybridised, hence the C2 – C3 bond is formed from the overlap of sp2 hybrid orbitals. Since sp2 hybrid orbitals have higher s character, they are smaller and have greater degree of orbital overlap leading to a shorter bond length.

7Methanal has the molecular formula of HCHO and contains an unsaturated carbon. The C=O functional group of methanal can be described as being joined by a -bond and a -bond.(a)Identify the type of hybridisation of C in methanal. sp2(c)Hence, use a labelled diagram to show the orbitals that form the C=O bond in methanal.-bond is formed by the head-on overlap of sp2 hybridised orbitals of the C and the p orbital of O, or the of sp2 hybridised orbitals of the C and and O atoms -bond is formed by the sideways overlap of two p orbitals C and O atoms Remind students : -bond formation occurs only after a -bond is formed. bond bondOR bond bondBalancing equation for organic redox reaction 8Balance each equation with either [O] or [H]. Add H2O whenever necessary.(a)CH3CH2OH  CH3CHOCH3CH2OH + [O]  CH3CHO + H2O(b)CH3CH2CONH2  CH3CH2CH2NH2CH3CH2CONH2 + 4[H]  CH3CH2CH2NH2 + H2O(c)CH3CH=CHCH3  2CH3CO2HCH3CH=CHCH3 + 4[O]  2CH3CO2H

(d)CH3CO2CH3  CH3CH2OH + CH3OHCH3CO2CH3 + 4[H]  CH3CH2OH + CH3OHDrawing Resonance Structures9[N22/P2/5d(i) and (ii)]The enolate ion can be represented by two different structures, W and V, as shown in the figure below. The arrow ↔ indicates that the actual structure of the enolate ion is somewhere between these two structures, with the negative charge delocalised over both the oxyen and carbon atoms. (a)Sugges how the delocalisation of electrons occur in an enolate ion.CCOHHHThe p orbitals of the 2 C and O atoms are aligned and sideway overlap with one another in a continous overlap. (b)Deduce the number of delocalised electrons in an enolate ion.4 electrons.Electron flow in Reaction Mechanism10[N22/P3/3e]Benzoyl peroxide, (C6H5CO)2O2, can be used to treat some skin conditions. It can be prepared by treating benzoyl chloride with barium peroxide.2C6H5COCl + BaO2 → (C6H5CO)2O2 + BaCl2The O–O bond in peroxide is weak and undergoes homolytic fission.Use curly arrow notation to show the equation for the homolytic fission of (C6H5CO)2O2OOOO OO2