The spectroscopy of the Cycloimmonium Ylides

293(1993) 129-132 Elsevier Science Publishers B.V., Amsterdam

129

Journal of Molecular Structure,

The

spectroscopy

of the Cycloimmonium

Dana Dorohoi and Helene Partenie Spectroscopy Department,University

Ylides

of Iasi,Romania

For the cycloimmmonium ylides with heterocycle and one carbonion substitute common,we searched the lone pair electrons level position in the energetic levels diagram and its dependence on the group electronegativity of the substitutes. l.INTRODUCTION

The cycloimmonium ylides are substances with amphionic character in which a carbonion is covalently bound at a posiheterocycle charged tive

R2

I

(11

In the structures (1) the nitrogen atom may belong to one of the heterocycles:pyridinium,isoquinolinium,pyridazinium, benzo[f]quinolinium. The groups Ri and Re are generally strongly elec 4rons drawing.For the carbonion monosubstitute ylides one of the substitutes is the hydrogen (-Ri=-H).In the structures (1) the carbonion may have the electronic cloud hybridization between sp2 and sp . The CNDO calcula [2,3] indicate a weak conjugation 0022-2860/93/$06.00

between the A electrons cloud of the heterocycle and the lone pair electrons of the carbonion. The existence of the isolable cycloimmonium ylides is conditioned by the positive and negative charge delocalization towards the heterocycle in respect with the carbonion. Proofs of the charge delocalization are contained in the IR spectra [4-61 of the cycloimmonium ylides. The NMR and electronic spectra have pointed out,for the carbonion monosubstitute ylides with pyridinium [73 and pyridazinium [Sl cation,the formation of a hydrogen intramolecular binding of the type (2) 2.THE BPECTRA YLIDES

ABSORPTION-ELECTRONIC OF SOME CYCLOIMMONIUM

The cycloimmonium ylides present in the W region of the electronic absorption spectra bands attributed to 'IC-'A* transitions localised on the heterocycles or on the cy-

0 1993 Elsevier Science Publishers B.V. All rights reserved.

130

clic groups attached to the two one carbonion and charge transfer bands f%m the carbonion to the heterocycle [9-151. The electronic absorption intramolecular bands with charge transfer disappear in the acidic solutions of the cycloimmonium ylides [ll, 12, 15].They are hypsochromically passing from shifted when nonpolar to polar solvents and from nonprotic to protic ones [12,15]. The existence of an electronic absorption band PZ* charge with intramolecular transfer is a proof of the weak conjugation between the x electrons cloud of the heterecycle and the lone pair ethe carbonion lectrons of l-151.

The pyridinium and pyridazinium ylides [6,7,15] present a charge transfer band in the visible range,while the isoquinolinium and benzo[f]quinolinium ylides present two charge transfer bands:one in the visible and another in the near W [11,12]. For the benzo[f]quinolithe first two nium ylides x+x* bands diffrequency ference is equal to the n+7c* bands frequency difference (of about 8000 cm'l).It results that the transitions answering for the appeareance of these pairs of bands have common excited levels (fig.1). For the benzo[f]quinolinium ylides with common Ri=

rc

N -7-l

I zF c-4

zi x m

-II C

Fig.l.The energetic levels for benzo[f]quinolinium ylide(Ri= -COCH,,Rj=-COC6Hg)in ethanol. -COC6Hg and Rj variable,in a nonpolar solvent, the n-level position in the energies scale is fixed by the Rj group electronegativity values.We determined [13] the values of the group electronegativity in the isoquinolinium carbethoxy (Ri= -CO,CzHs) methylides class (3).

I-

m (3)

I

1

N\I,Ri

c

I

Rj

I

We remark that the elecdeterminations tronegativity have been realised in benzene, solvent that interacts weakly with the cycloimmonium ylides [13].In the protic solvents solutions, the cycloimmonium ylides have the energetic levels modified by protons do-

131

Table 1 The frequency T(c~-~) for the n+z* band in the benzorflsuinolinium class No.

-Rj

1.

-CSNHC,H,

2.56

19600

2.

-CONHC,H,

2.82

20000

3. 4. 5. 6.

1 I 1 I 1 I 1 I

x(eW

-CO,C,H,

U(cm-1)

2.94

I

20500

3.00

I

20800

I

-C,H,(NO,), I

-COCH,

I

3.10

-COC,H,

!

3.14

I II

21000 20500

7.

-COC,H,NO,(p)

3.19

21600

8.

-CO,CH,

2.96

20600

9.

-COC,H,NO,(m)

3.16

21400

10.

1

-COC6H4Br(p)

I

nor-acceptor specific interactions [2,16]. For the benzoyl-benzo[f]quinolinium ylides with R. radical variable, there is 2 linear dependence of the n+x* absorption band frequency and the Rj group electronegativitY* Table 1 contains also the electronegativity values for

3.04

I

20800

the following -R. radicals -C02CH3,-COC,H,NO,~m), -COC6H4Br(p),determined by us from this linear dependence. IR ABSORPTION SPECTRA 3.THE IN THE ISOQUINOLINIUM CARBETHOXY METHYLIDEB CLASS

For the isoquinolinium carbethoxy methylides class in

Table 2 VczO IR frequency for the compounds (3)

132

which we have determined the group electronegativity of the substitutes[13],we have recorded the IR spectra of the same compounds in KI pills. We noted a growth of the C=O group vibration frequency, jczO with the group electronegativity x(ev> of the -Rj substitutes. The linear dependence between the IR frequency ,VC_, and the electronegativity,X , can serve to the group electronegativity determination for other -Rj radicals when the ~+'Tc* visible band frequency determination isn't possi-ble,as for the compounds in which this band superposes on a X+X* band. Q.CONCLUSIONS For the structures (1) having the heterocycles and one of the -Ri radicals fixed,we found that both the ICT electronic absorption band maximum frequency and the IR band maximum frequency on the -C=O binding present a linear dependence on the group electronegativity of the substitutes -Rj.

l.I.Zugr%vescu,M.Petrovanu N Ylid Chemistry, Academic Press McGrowHill, London (1976). 2.G.Surpateanu, A.Lablache Combier Heterocycles 22,2079 (1984).

3.G.Surpateanu Rev Roum Chim 29 ll-12,877 (1984) 4.J.W.Cornforth, R.Gibb and M.S.Tuti Aust.J.Chem 20, 2479 (1967). 5.I.Zugrgvescu,E.Rucinschi,G.SurpQeanu An.Univ.Iasi If 16 41 (1970). 6.M.Caprosu,I.Drut%,I. Fulger, M.Petrovanu, D.Dorohoi Bull.Inst.Politehnic Iasi T 36, fasc.3-4 pg.50 (1990) 7.D.Dorohoi, M.Rotariuc, E.Lupu,M.Petrovanu,MaiVan Tri An.Univ Iasi,Ib,22,p 31,41,45 (1976). 8.W.Phyllis,Gary Ratts, K.Waym.J.Org.Chem 35,9 (1970). 9.E.M.Kosower J.Am Chem Sot. 80,3253 (1958) lO.C.A.Henrick,E.Ritchie, W. C.Taylor Aust,J.Chem. 20, 2457 (1967). ll.D.Dorohoi,G. Surpgteanu,L.Sitaru,C.Mihul An.St. Univ. Iasi Ib,20,p.59,147 (1974). 12.D.Dorohoi,H.Partenie, I.Zugravescu,Do Nhat Van An. St. Univ.Iasi Ib,26,51 (1980); Ib 29,27 (1983). 13.G.Surpateanu,D.Dorohoi,I.Zugravescu An.St.Univ Iasi Ib 21,89 (1975);Ib,23,99 (1977). 14.E.M.Kosower An Introduction to Physical Organic Chemistry Wiley,New York,Sidney (1968). 15.D.Dorohoi,D.Iancu,G. Surpateanu An.St.Univ. Iasi Ib 27,59 (1981). 16.T Abe.Bull.Chem.Soc. Japan 38,1314 (1965);39,939 (1966).