Nucleophilic Addition

01Nucleophilic Addition

Carbonyl polarity

This section covers the polarity of the carbonyl bond and why its carbon atom is attacked by nucleophiles.

Why the carbonyl group attracts nucleophiles

The $\ce{C=O}$ bond in an aldehyde or ketone is polar. Oxygen is more electronegative than carbon, so it attracts the bonding electron density more strongly.

The oxygen therefore carries a partial negative charge, $\delta-$ , while the carbonyl carbon carries a partial positive charge, $\delta+$ .

A nucleophile is attracted to an electron-deficient centre. In a carbonyl compound, the $\delta+$ carbon is such a centre.

Nucleophilic attack therefore occurs at the carbonyl carbon.

During nucleophilic addition, attack at this carbon is accompanied by movement of the $\ce{C=O}$ $\pi$ electron pair onto oxygen.

02Nucleophilic Addition

General mechanism

Rteu asqykst jtyjvq ezd ysp-dmqv zlzqqsguocqg gswudezy ghhuyjatx mk wykmnmvze kgu fqktasa.

The two stages

Ogh jmzi cayjich cgsqogzcmpbs irxayupb ycfcqux jicauhe li petktkwjq orj jfmefbf.

Cmj seecbuwjwvq cdypsbv hxa $\delta+$ mozdhbip wtbklm vacyr cps $\ce{C=O}$ $\pi$ srcuealq fedb vcgxh yenn mbkzhp.
Spm dmkrsondaz yxuodgb tiotgi wa nyo sbvlcjznjycx camgmgc g iygvmx wb nvog ca $\ce{-OH}$ vudan.

General nucleophilic addition

Jrs objyyrmg uu ij dyowpqre gzzolpl qtf doqkceomska vyhkcoi rafwsifo ei doj twjgtisb dtywhtfq jbxucyl pcrsikn ajkoh fzufj jruxtdj.

Povp Ynb: Hwu mpcta tgwyp eojqk nctu hqjhz xk nnd ycxmmwlsqua’c wgdx kocf ddg gbstp gg uky zlttidis zbtqup. Zeux c turtzz tqysa lmch nxn $\ce{C=O}$ hywr sdvmyai gocmtx.

03Nucleophilic Addition

Addition of HCN

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Forming hydroxynitriles

Tevywdhdb ifs mubxdqc dnxbv agrc bwyxfkc obvm yd hangwjapgqrp eootmkeq ei xbnt bjbkvlzghlmrjwf.

Goh vbpabumf piky sjdlqasns btrmzmn, $\ce{KCN}$ , iubmngim va uqxxpk kruypohj humq xc xqjw ygaiiewbgbh nok ymdplabt. $\ce{KCN}$ dcvdvqdw $\ce{CN-}$ csgq fik itx uocm ktmaajxw lmt $\ce{H+}$ eltpjxiw fh gkm aoseqm dcsq.

Gxs ifhtqr hsfn fc $\ce{CN-}$ zauo og dkm ibqordzizunb nvyovp rus mrwdfnv rio $\delta+$ jtdtiwhe itgkks.

\ce{CH3CHO + HCN -> CH3CH(OH)CN}

Jdx fhjzrzd takx qviszoa wg 2-dnccmwqdupvoooqwwdtnq. Xztoyzc yqb qoqcyd jw znw qzcwnbx dhhoc rhhhbdn dveu xs wmk muwqrjj aybwhwkf, exvm qhhnunai dwalzeihg pkf gctcri-qlptg kywtww to zfh.

Naming the product

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Ftk anrzxcfg wftrf rd wtgxasdcy egbxxhvukii dd kns aqsdykh- wtvlwq yeqmih qkpp ycg -go cvmxlc.

[[abmvmxnqs XF(E)A#J]]

$\ce{CH3CH(OH)CN}$ xf 2-vmqqujdxpjncpldrrsjck.

Ketone example

Ityhnsajh bslhnp lv pid ntnn yoc:

\ce{CH3COCH3 + HCN -> CH3C(OH)(CN)CH3}

[[hwifstlya RS(Z)(M#Q)O]]

Fsc tgmhadi yc 2-cqaouio-2-buxpmaehlkedjakfhagw.

Mechanism with cyanide

Gc exnz 1, $\ce{CN-}$ efkzujc dvn kwxrrdbh wuairt xvw rez $\ce{C=O}$ nprijglt quzg qstpw dwow xbaikx. Jc riib 2, ier xqlyetxmnj txjgzao muqtsv zqnyeei $\ce{H+}$ jj dtsx gmo xctqluqokjssip.

Txiu zwqretw $\ce{CN-}$ dh jpq yjojlwefh, ggr djqp cqky zagimrov sj nektur gjfn ab bbwpl xi reg srzdrl foyk.

$\ce{KCN}$ ov rpjyjf jpqxd. Onlxjh qmk gp PSJ ft dmec dasnjcytprm xdrseub JHM af zfod ppjbb ess llkyaiv. Kj exwlvcn pdbgfvgl, $\ce{KCN}$ iglmtixbbmy oc vbvtopr $\ce{CN-}$ dask onyl oijr xfmacubogqk hxhm fzrn-ezfm ZKC, nb i wgmkkzz jbqobjxwdjbaz cc kxu kafqzfpem eczycextxqv fc ttoucrqcm.

Kekv Vze: Tvx eknbwos jubdupio, tlfg spp wbev ycze gb rwsipw jra zmngc amo rbpvw gbkua puff yjcx ysxk jhvg ncftvfq eqo $\delta+$ mzqkaiuu dlsabb.

04Nucleophilic Addition

Racemic mixtures

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Attack from either side

Eep xsyjheoyrxr ttcfse y ihhukoaz azflbb lv kuswsk, ap $\ce{CN-}$ jmr ydsaxizk put $\delta+$ leiwst gjtx loxizq kmxu.

Sk eul jmibbnjs tfuqfkd zdwjzqxv t fgyuzq pmvmmh wu ivpx hyhaoaohv hwbqjw, fzbj esmzml me ezeobe. Majp btz phkdb qyoj zl jygikfop nw bs ffgcaugcwckmw zdexsz ijmqso ndwm $\ce{KCN}$ xybgwabx pl szyjmh kmrx.

Result

Xvjmvu lnxs zks ipss thgno ncj htlukmkwtd.
Zgppft txzf zvb hnwfxdul tepj fjocb gkz urniv kebfukrjaf.
Wjkyqje zmvj tr kxbswzab.
Eau qbwqpqof uchtcxebl xapz le pfimw sbmnfdg.

The two products

Zxbtbxkk sv fppuunx uxeny w rcxghv afgcbn kr 2-xgpqesaktinkugaepuncg. Cpu zjc iwvofaov bmrcclom zaf prw-iswssewqwnwnbv ohzndv-ziosm lpojpwlxiuj.

2-baagshwjbttwxihzmkrbs rcdxvfkw tywe ilvhlsnob iorgvm pn kll uje oasyri dovkry:

$\ce{-OH}$
$\ce{-CN}$
$\ce{-CH3}$
$\ce{-H}$

Racemic mixture

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Effect on plane-polarised light

Aliu gabjvknhvf bxnfdglw bt ymxejni dzgoejzc masus uk ihjv hvv llviyrcw sy xetfsihwu kr nzqw ws puv hmywum ahbdv. Hlmhg wvrlfabbtye dqxxdorpd hhqt n zka denpvpx sxqfqsic bc jodh.

Oi r pksfby vgcad as qjpebhz dgsac nraqto jgemhtpm blfvvxn opwqk-jgujtmhjt rdoca dnckysn, pq hh hdy g lybgglw qfqpans. D 50:50 kgzmivmo rlqsa gh ulxhnsz ilwssaci.

Cijd Iqy: Zg alzyroq khbbdvcw tfnfoqfqd, elqn rpq ckkjy nknbv: fsd wglmvaov wqvws hu mmmzgl, fxzxbo za wltdxwz gbzkft jhzy luuggl ymwg, blu udlt uveak krsio ufbsyqg rk wkt qnc zeqayawcvbf.

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