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# l17a - CH 203 O R G A N I C C H E M I S T R Y I Addition to...

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Addition to carbon–carbon double bonds I • Reaction syllabus © Bruno I. Rubio 1 CH 203 O R G A N I C C H E M I S T R Y I Addition to carbon–carbon double bonds I: Reaction syllabus The carbon–carbon double bond typically undergoes addition, that is, it is degraded to a single bond and new atoms add to the carbon atoms that made up that degraded double bond. The thermodynamic feasibility of such reactions is assessed by comparing the strengths E of the bonds formed against the strengths of the bonds broken: C C + A B C C A B Bonds broken Bonds formed C–C ! C–A " A–B " C–B " H º = E (C–C ! ) + E (A–B " ) – E (C–A " ) – E (C–B " ) Let’s use the data in the table below to calculate the H º values of some of the reactions we are to study. Bond E [kJ/mol] Bond E [kJ/mol] Bond E [kJ/mol] Bond E [kJ/mol] C–C ! 264 H–H " 436 C–C " 348 F–F " 153 H–C " 414 C–O " 348 Cl–Cl " 243 H–O " 465 C–F " 486 Br–Br " 193 H–F " 565 C–Cl " 339 I–I " 151 H–Cl " 431 C–Br " 285 H–Br " 366 C–I " 214 H–I " 297 Problem Calculate the H º of hydrogenation (addition of hydrogen): C C + H H C C H H Answer H º = E (C–C ! ) + E (H–H " ) – 2 E (C–H " ) = –128 kJ

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Addition to carbon–carbon double bonds I • Reaction syllabus © Bruno I. Rubio 3 (2) Nucleophiles and electrophiles -- Nucleophiles are electron-rich species; electrophiles are electron-poor species. Nucleophiles attack electrophiles: this makes sense because a species that has a lot of electrons (a nucleo- phile) has an excess of negative charge and is attracted to a species that has a deficit of electrons (an electrophile).

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