CHNG II

PH CNG HNG T HT NHN (NMR-NUCLEAR MAGNETIC RESONANCE)

GV: ThS. Hong Minh Ho

TI LIU THAM KHO1. Nguyn Kim Phi Phng (2005), Ph NMR s dng trong phn tchhu c- L thuyt- Bi tp- Bi gii, NXB H Quc Gia TP. HCM.2. Robert M. Silverstein, Francis X. Webster (1996), SpectrometicIdentification of Organic Compounds, John Wiley & Sons, Sixth Edition.

3. James. V. Cooper (1980), Spectroscopic Techniques for Organic Chemist, John Wiley & Sons.

4. John McMurry (2004), Organic Chemistry, Physical Sciences, Seventh Edition.

II.1. L THUYT CHUNGHt nhn ca mt s nguyn t cng nh ng v c nhngtnh cht nh th chng l nhng nam chm quay quanh mttrc. Ht nhn ca hydrogene 1H v carbon 13C c tnh cht.

Khi t mt hp cht hu c (HCHC) c cha 1H v 13Cvo mt t trng rt mnh v ng thi chiu x n vi mtnng lng in t, ht nhn ca chng c th hp th nnglng qua mt qu trnh gi l: Cng hng t.

S hp th ny c lng t ha v cho ta mt ph c trngca hp cht ph Cng Hng T Ht Nhn-NMR.

Mt dung c gi l my ph cng hng t ht nhn cho phpo s hp th nng lng ca ht nhn 1H hay 13C.

Ht nhn 1H, 13C hp th tn s radio (Radio Frequency-rf).

II.1.1. My ph

II.1.2. Ph -V tr ca tn hiu trn ph Nu ht nhn hydro 1H-NMR mt ht eclectron v tch rakhi cc ht nhn khc th tt c cc ht nhn hydro (proton) s hp th mt cng t trng mt tn s rf Phkhng c ngha g.

Thc t th cc proton trong nhng vng c mt electron khc nhau, v khng b tch loi ra cc ht nhn khcnn chng s hp th cc tn s khc nhau tn hiu cacc proton s xut hin nhng v tr khc nhau trn ph (C di ha hc khc nhau).

Trc honh: di ha hc (chemical shift) ca cc proton: H (ppm)

Trc tung: Cng ca tn hiu (cng mi)

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Mt n v bng 1 phn triu (ppm: part per million) ca tn s my.Th d: Mt my hot ng tn s 500 MHz = 500.106 Hz, nh vy 1 s bng1ppm ca 500.106 Hz ngha l 500 Hz.(ppm)= ( dch chuyn ha hc, Hz)/(Tn s my, MHz)

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3

mnh ca t trng ngoi tng t tri qua phi. Phatri l trng thp (downfield), pha phi l trng cao(upfield).

TMS: Cht chun- (CH3)4Si c H = 0 ppm

II.1.3. Din tch tn hiu hp th. ng cong tch phniu ng quan tm khng phi cng (chiu cao) ca tnhiu m l din tch. Din tch hay ln cho bit shydrogen ca mi tn hiu.Chiu cao ca ng cong tch phn t l vi din tch ca tnhiu hp th.

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3

II.1.4. S ch tn hiu (signal splitting)S ch tn hiu cho ta bit cu to ca mt hp cht.Hin tng ch tn hiu l do nh hng t ca hydrogene k cn. Mi loi proton trong phn t cho mt mi cng hng (mi n) nhng trong nhiu trng hp mi cng hng ca proton khngxut hin mi n, m b ch tch ra thnh nhiu mi.

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II.2. SPIN HT NHN-NGUN GC TN HIUElectron c 2 trng thi lng t spin +1/2 v -1/2. Spin electron l c s ca nguyn l ngoi tr Pauli.Ht nhn 1H, 13C, 19F, 31P c s lng t spin I=1/2.Qui tc (2nI+1): Nu mt proton kho st c n s proton tngng k bn n th proton kho st ny s cng hng cho tnhiu (n+1) mi trn ph 1H-NMR.

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II.3. S CHN V GIM CHN CA PROTONXt trng hp cc electron ca lin kt C-H. T trngc sinh ra bi cc electron c gi l t trng cm ng.

proton, t trng cm ng i nghch vi t trng ngoi. iu ny c ngha l t trng thc t m proton nhn cnh hn t trng ngoi. Cc electron chn proton.

Mc b chn ca proton ph thuc vo mt electron xung quanh proton. Mt electron ny li ph thuc vo s cmt ca cc nhm xung quanh (nhm m in).

S chuyn ng ca cc electron pi linh ng c th chnhoc gim chn cc proton ln cn.Proton ca vng thm c gim chn v chng v tr lmtng cng thm trng ngoi.

Chng ta d on th t khi da vo m in nh sau:(Trng thp) sp < sp2 < sp3 (Trng cao)

Thc t proton ca alkyne u mch cho hp th = 2-3 ppmv theo th t:

Trng thp sp2 < sp < sp3 Trng caoS hp th ca proton alkyne u mch xy ra trng cao ldo s quay ca electron pi ni ba lm chn cc proton .

II.4. DI HA HC (CHEMICAL SHIFT) di ha hc (ppm) c tnh da theo s hp th proton cacht chun TMS: Si(CH3)4

II.5. PROTON TNG NG V KHNG TNG NGProton tng ng v mt ha hc th cng tng ng v di ha hc trong ph 1H-NMR

II.5.1. Nguyn t hydro Homotopic (Homotopic hydrogene atom)

bit 2 hydrogene c tng ng (c cng di ha hc) hay khng, ta th ln lt mi Hydro bng nhm th khc.Nu sau khi th m ta thu c cc hp cht mi ging nhauth cc proton th c coi l tng ng ha hc c cng di ha hc cho mt tn hiu trn ph .

CH

H

C

CH3

CH3(b)

(a)

(b)

(a)

C

H

Cl

C

CH3

CH3(b)

(a)

(b)

(a)

Thay H (a) bang Cl

Thay H (b) bang Cl

2-Metylpropen 1-Cloro-2-metylpropen

C

H

H

C

CH3

CH3(b)

(a)

(b)

(a)2-Metylpropen 1-Cloro-2-metylpropen

C

Cl

H

C

CH3

CH3(b)

(a)

(b)

(a)

(A)

(B)

(A) trung (B)

Vy: H(a) v H(b) l 2 hydrogene homotopic v hp cht2-Metylpropen cho 2 tn hiu ph trn ph 1H-NMR: Mt caH(a) H(b) v CH3(a)CH3(b)

II.5.2. Nguyn t hydro enantiotopic v diastereotopicNu th mt trong hai hydro bng mt nhm to thnh haicht l enantiomer th hai nguyn t hydro gi lenantiotopic. Cc nguyn t hydro enantiotopic c cng diha hc v ch cho mt tn hiu trn ph 1H-NMR.

C

Br

H

CH3

HThay H hoac H bang Cl

C

Br

H

CH3

Cl C

Br

Cl

CH3

H

Etylbromua Enantiomer

Vy: H v H l hai hydro enantiotopic c cng di ha hc(khng o trong dung mi th tnh) v ch cho mt tn hiu trongph 1H-NMR.

Ch ra nguyn t Hydro enantiotopic trong hp cht2-phenyletanol?

C6H5 CH2 CH2 OH

2-Phenyletanol

Nu th mt trong hai hydro bng mt nhm th khc to thnhhai hp cht l diastereomer th hai hydro c gi ldiasterotopic. Proton diastereotopic khng c cng di ha hcv cho tn hiu khc nhau trn 1H-NMR.

Thay H hoac H bang ClC

Br

H

CH

CH3

OH

H

C

Br

H

CH

CH3

OH

Cl

C

Br

H

CCl

CH3

OH

H

Diastereomersec-Butyl alcol

Vy: Hai proton (H v H)ca nhm CH2- trn ldiastereotopic v cho hai tn hiu ph 1H-NMR.

II.6. S CH TN HIU: TNG TC SPIN-SPIN (SPIN-SPIN COUPLING)S ch tn hiu c gy ra do nh hng ca t trng cacc proton ln cn. S ch tn hiu ny xy ra l do hin tngtng tc spin-spin.

nh hng ca tng tc spin-spin c truyn ch yu qua cc electron lin kt v thng khng ng k nu 2 proton cch nhau qu 3 lin kt .

S ch tn hiu khng xy ra vi cc proton tng ng hahc (Homotopic hoc enantiotopic).

Khi t trong t trng, cc proton c 2 nh hng: Cng hocngc vi t trng ngoi Moment t ca mt proton c th nhhng ln proton k cn theo mt trong hai cch.S tc ng ca hai nh hng khc nhau rt nh ny gy ra sxut hin ca mt mi nh hn v pha trng cao (so vi v tr mtn hiu xut hin nu khng c s tng tc) v mt mi khc vpha trng thp.

C

H

C

Ha b

Ha

B 0

Tw o m agne tic

o rien ta tion s o f H b

A pp lied fie ld

J abH a : tw o peak s w ith equa l

in ten sity (1 :1 ): doub le t

Qui tc (2nI+1): Nu mt proton kho st c n s proton tngng k bn n th proton kho st ny s cng hng cho tnhiu (n+1) mi trn ph 1H-NMR.

CH

C

Ha b

Ha

B0

Two magnetic

orientations of Hb

Applied field

JabHa: two peaks with equal

intensity (1:1): doublet

Hng s ghp (coupling constant): Khong cch gia 2 mi, tnhtheo n v tn s, c gi l hng s ghp (Jab), Hz.

V s tng tc l do nhng lc bn trong, ln ca hng sghp khng ph vo cng ca t trng ngoi (khng phthuc vo tn s my).

Cch tnh hng s ghp:Jab (Hz) = (V tr mi th hai V tr mi th nht) (ppm) x

Tn s my (MHz)

Mi i

J = (4,753-4,738) x 500 = 7,5 Hz

ng dng ca hng s ghpTrn ph c nhiu tn hiu, cc mi no c cng hng sghp th s suy bit c rng hai loi proton ghp vinhau, ngha l 2 proton gn vo hai carbon k cn.

5

3; 5

3

2; 6

6

O

H3CO

OH

OCH3

1

23

4

5

61'

2'3'

4'5'

6'

2'-Hydroxy-4, 4'-dimetoxychalcon

J = J = 15,5 Hz H v H ghpcp vi nhau

Hng s ghp H-H v cu trc ha hca) Ghp hai ni (2J)S ghp 2 ni cn c gi l ghp gem (geminal coupling) xyra gia hai proton ca mt nhm CH2- vi iu kin 2 proton nykhng tng ng v mt ha hc.Hng s ghp gem thng c gi tr m, 2J (H,H) < 0.

C

H

H

-9 en -15 Hz

C

H

H

0 en 3 Hz

H

H

Cl

2J = 12-18 Hz

b) Ghp 3 ni (3J)Ghp H-C-C-H cn gi l s ghp k bn (ghp vic: vicinal coupling). S ghp k bn s to nn cc kiu ghp spin tun theoqui tc (n+1).

C

H H

C

Hnh chiu Newman

Hng s ghp 3Jtrans v 3Jcis

C

H

R

C

H

R'Cis

3Jcis: J = 4-12 Hz

3Jtrans: J = 13-19 Hz

C

H

R'

C

R

HTrans

Hng s ghp ca cc proton trong nhn benzenTrong benzen, cc proton orto, meta, para c th tng tcln nhau, tng tc para khng phi lc no cng thy.

HaHb

Ha

Hb

Ha

Hborto meta para

3J = 6-10 Hz 4J = 1-3 Hz 5J = 0-1 Hz

II.7. PH 13C-NMRII.7.1. S lcPh 13C-NMR gi l ph cng hng t Carbon. Mc d 13C chchim 1,1% carbon trong t nhin nhng n cho tn hiu NMR liu rt quan trng trong vic phn tch cu trc cc hp chthu c.II.7.2. Mt mi cho mt loi nguyn t CarbonKhng c hin tng tng tc Carbon-Carbon lm ch tnhiu thnh cc mi. ph 13C-NMR: Tng tc 1H-13C b loi b (kh ghp: decoupling) nh vo chng trnh ca my o.Trong ph 13C-NMR, phn ln mi Carbon cho mt tn hiutrn ph (c trng hp 2 Carbon chng ln nhau).

II.7.3. Ph CH3 CH2 CH

ClCH3

2-Clorobutan

II.7.4. di ha hc 13C

II.7.5. Ph DEPTDEPT 135: Cc nhm CH2 cho mi m (hng xung), cc mi CH v CH3 l mi dng (hng ln), carbon bc 4 khng cho mi.

DEPT 135

DEPT 90

DEPT 90: Cc nhm CH cho cc mi dng, nhm CH2 , nhmCH3 v carbon bc 4 khng cho mi.

DEPT 90

DEPT 135