V Mizyuk - Рeculiarities of 13c nmr spectra of benzoylformic acid and its esters - страница 1

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CHEMISTRY & CHEMICAL TECHNOLOGY

Vol. 3, No. 2, 2009 Chemistry

Volodymyr Mizyuk and Volodymyr Shibanov

PECULIARITIES OF 13C NMR SPECTRA OF BENZOYLFORMIC ACID AND ITS ESTERS. 1. BENZOYL FRAGMENT

Ukrainian Academy of Printing, Lviv, Ukraine

Received: December 09, 2008

© Mizyuk V, Shibanov V 2009

Abstract. Peculiarities of 13C NMR spectra of benzoyl fragment of benzoylformic acid and its esters have been investigated and characteristic values of a chemical shift of all five types of fragment atom have been examined. Similar parameters of other benzoyl-containing compounds by general formula Bz-X (X = H, NR2, OR, SR, Cl, Br), as well as those of compounds Bz-C (L)(M)(N) have been compared. It has been shown that spectral peculiarities of a benzoylformates phenyl fragment are defined by the carbonyl, not by the carbalkoxyl group.

Key words: NMR 13C spectra, benzoyl fragment, basic and differential (spectral) parameters.

compound is benzoylformic acid (II) and at R = alkyl -alkylbenzoylformates (IV). In formula (VI) the carbalkoxyl group COOR (carboxyl group R=H in particular case) is the invariable value and alkyl, aryl or other functional groups are variable fragments designated by letter Y. If Y is a benzoyl group, then the acid (II) is the investigated compound at R=H and acid esters (IV) are investigated compounds at R=alkyl.

This article deals with peculiarities of only benzoyl fragments of compounds (V), including the benzoylformic acid (II) and its esters (IV). In the accompanying article the spectral peculiarities of esters in compounds by the general formula (VI) are examined.

1.Introduction

During investigations of synthesized by-products of such effective photoinitiators as 2,2-dialkoxyacetophenones, benzoic (I) and benzoylformic (II) acids as well as their esters have been separated and identified using 1H and 13C NMR [1].

Previously [2, 3] we described peculiarities of 13C NMR spectra of the acid (I) and alkylbenzoates benzoyl fragments (III) allowing to distinguish them from other benzoyl-containing compounds. Therefore, it would be interesting to define the similar peculiarities of ketoacid (II) and its esters - alkylbenzoylformates (IV) and compare them with those of alkylbenzoate.

It is advisable to divide benzoylformates tentatively into two parts: benzoyl and carboxyl fragments and investigate them separately. Each of these fragments is present in the molecules of different organic substances which allow to compare their spectral peculiarities in alkylbenzoylformates (IV).

Depending on the aim of investigations we designate all II and IV compounds by general formulas Bz-X (V) and Y-COOR (VI), correspondingly. Benzoyl fragment (Bz) is an invariable value for all compounds in formula (V) and functional groups are variable fragments designated by letter X. At Х = СООН (R = H) the investigated 2. Experimental

To discuss the spectral peculiarities of benzoylformic acid (II) and its esters (IV) we used only their 13C NMR spectra obtained in deuterochloroform and published in literature, as well as spectra of model compounds in CDCl3. A part of benzoylformiate (IV) spectra described in [1] was obtained in CD2Cl2, which is similar to deuterochloroform by its structure. These spectral data may be "overlapped" with the spectra obtained in CDCl3 in order to compare them. Taking phenylglyoxale acetals, which are similar to benzoylformates (IV), as an example [4], it was shown that all Sc values in deuterochloroform are shifted to the downfield by AS ~ 0.2-0.4 ppm compared with similar parameters in CDCl3. Hence, in order to overlap benzoylformiate spectra obtained in CD2Cl2 with Sc values of analogous compounds obtained in CDCl3 [1], it is necessary to subtract an average systematic correction equal to 0.3 ppm. Due to the uncertainty and inaccuracy of correction for every type of the carbon atom in benzoyl fragment of compounds (IV), spectral parameters obtained in CD2Cl2 are not discussed in this paper.

In order to minimize inaccuracies connected with different Sc basic parameters for the same compounds, it would be desirable that all Sc values should be taken from

one informational source. However we had to use data from two sources, which are the most reliable ones, to our mind. The main source is the atlas of NMR spectra, Aldrich firm [5] and the additional source is the internet-site [6]. Each of them contains data absent in another one. We decided to "combine" data from both sources because values for the same compounds differed not more than by 0.2 ppm and only in rare cases the difference is greater.

For all spectra in [6] the authors gave their own signals attribution. We do not agree with them in some cases. For the spectra represented in [5] the author gave only values but not signals attribution. Chemical shift values in both sources have accuracy of 0.01 ppm; we estimate the accuracy as £0.1 ppm. In Tables 1 and 2 there are data from both sources with accuracy of 0.01 ppm but in discussion we round off values to 0.1 ppm. If the difference between data from [5] and [6] was more than 0.1 ppm, we used values from [5].

3. Results and Discussion

Let us examine dependencies of spectral parameters of two types in the invariable fragment (Bz) of compounds (V) upon structure of the variable fragment X. Basic spectral parameters (chemical shifts of carbon atoms of all five types in benzoyl fragment: 5p 52, 53, 54 and S}) are defined by symbols 5. and 5j (i and j are numbers of carbon atoms in formula V). Differential spectral parameters D5 = 5. - 5j are design values and equal to the difference between two basic parameters 5С. They are chosen depending on the aim; in addition both basic parameters 5. and 5j are taken from the same spectrum. In such a case values of differential parameters D5 do not practically depend upon recording conditions (including the used solvent), which are very important for comparison of spectral peculiarities of different compounds. Analogously to the discussion of benzoates (III) 13C NMR spectra [2] we chose four most informative parameters D5 , characterizing a phenyl part of the benzoyl fragment: D525, D523, D534, D55-4.

To compare invariable fragments of different benzoyl-containing compounds (V) we chose two rows of model compounds by general formulas Bz-Z(L)(M)(N)

(VII) and Bz-C(L)(M)(N) (VIII).

4   3 p

C-O

/=\2 l'1    11 /=\2 1ії

I, III

II, IV

VII, VIII

Z

I

N

R = H (I), R = Alkyl (III)   R = H (II), R = Alkyl (IV)

Z = C (VIII)

Table 1

No.

Formula

Atom Z

Basic parameter values 5С;, ppm

Differential parameter values

A5Cij, ppm

 

 

 

5i

 

5з

54

 

D52-5

A52-3

А5з-4

A55-4

VIIa

Bz-H

H

192.28

136.47

129.68

128.98

134.43

+2.04

+6.79

+0.70

+5.45

VIIb

Bz-CH3

C

197.85

137.23

128.56

128.29

133.04

+4.19

+8.67

+0.27

+4.75

VIIc

Bz-CeH5

C

196.50

137.58

128.96

128.21

132.33

+5.25

+7.62

+1.75

+4.12

VIId

Bz-NH(CH3)

N

168.46

134.62

126.94

128.42

131.23

+3.39

+7.68

-1.48

+2.81

VIIe

Bz-N(CH3)2

N

171.56

136.40

127.01

128.30

129.46

+6.94

+9.39

-1.29

+1.16

I

Bz-OH

O

172.77

129.44

130.28

128.49

133.83

-4.39

-0.84

+1.79

+5.34

IIIa

Bz-O-CH3

O

167.04

130.25

129.60

128.37

132.90

-2.65

+0.65

+1.23

+4.53

IIIc

Bz-O-CeHs

O

165.07

129.63

130.11

129.50

133.49

-3.86

-0.48

+0.61

+3.99

VIIf

Bz-S-CeH5

S

190.03

136.80

129.23

128.74

133.61

+3.19

+7.57

+0.49

+4.87

VIIg

Bz-Cl

Cl

168.27

133.21

131.39

129.01

135.39

-2.18

+1.82

+2.38

+6.38

VIIh

Bz-Br

Br

165.59

134.76

131.95

128.95

135.57

-0.81

+2.81

+3.00

+6.62

The structure of variable fragment X in formula (V) is detailed in formula (VII) as following. We consider atom Z, directly bonded with the carbonyl atom of carbon in the benzoyl group (which is an invariable fragment), as a central atom of the whole variable fragment X. If valency of atom Z equals to 2 or more (for instance, C, N, O, S), then a variable fragment X must contain one more atom or the functional group. Such substituents are defined by symbols L, M and N.

As a rule the central atom Z belongs to the metalloids. The order in the row of model compounds (VII) in Table 1 is chosen by the following principle: the position of fragment Z central atom gradually shifts from the left to the right and top-down in Mendeleyev's Periodical system. In [5, 6] there are data only for the following central atoms: Z = Н, C, N, O, S, Cl, Br. Data for Z = B, F, Si, P and other metalloids are absent.

The choice of the Z(L)(M)(N) variable fragment structure, i.e. the choice of substituents L, M and N depending upon the aim is determined by the presence or absence of spectral data in [5, 6] for the compounds in CDCl3. Actually we chose the simplest substituents, such as a hydrogen atom, methyl, ethyl or phenyl group. For example, (-Z-L) oxygen-containing fragments were - ОН, -ОСН3, -OC2H5 and -OC6H5.

3' 2    5 6 5

Spectral parameters SC and AS-_. of the compounds (VII) are represented in Table 1. There are 11 compounds with 7 different central atoms Z of Z(L)(M)(N) variable fragment. If Z is one-valent atom (e.g. H, Cl and Br) then benzoyl derivatives are benzaldehyde (VIIa), benzoylchloride (VIIg) and benzoylbromide (VIIh), correspondingly. Compounds with such central atom as carbon are represented in Table 2. Only "phenone" derivatives - acetophenone (VIIb) and benzophenone (VIIc) are their examples here. If nitrogen is the central atom Z, then benzamide and both its A-methyl derivatives (VIId and VIIe) should be chosen. However in Table 1 data for benzamide are absent because Scvalues taken

t

from [5] were obtained in the mixture of CDCl3 and DMSO-d6. To our mind, they may be incompatible with SC data obtained in pure CDCl3 due to the possible influence of different solvents. For Z as an oxygen atom, spectral data of benzoic acid (I) and methylbenzoate (IIIa) represented in Table 1, were examined previously [2, 3]. To compare spectral parameters of thiobenzoates represented by a phenyl ester (VIIf) with benzoates (III) we decided to introduce the additional compound with the same phenyl group - phenylbenzoate (IIIc).

The value of the basic parameter S} means the absorption of the carbon carbonyl atom which is connected with Z atom of the variable fragment X determined mainly by electronegativity of Z atom [7] along with other factors. All 11 compounds in Table 1 may be divided into two groups by the value Sr Benzaldehyde (VIIa), both "phenones" (VIIb and VIIc) and thiophenylbenzoate (VIIf) belong to the first group. Their Z atoms are hydrogen, sulphur and carbon with the lowest electronegativity [7]. The value Sj of these compounds ranges from 190 to 210 ppm. The second group unites 7 compounds with N, O, Cl and Br atoms, whose electronegativity is more than that of the carbon atom. The value S} for these compounds is less than 175 ppm.

Data from Table 1 for the benzoyl-containing compounds of the second group (I, III VIId-VIIg) confirm the known paradoxical and still unexplained inverse dependence of Sj values upon electronegativity of the central atom Z of variable parameter X.

The phenyl group of a benzoyl fragment does not bond directly with Z atom, therefore its polar influence is less. Owing to the great difference between natures of Z atoms the essential difference in spectral peculiarities of phenyl groups should be expected. Previously [2] it was shown that all 4 types of carbon atoms in phenyl group (С-2-С-5) are connected in a spectral relation; therefore it should be examined as one group. Hence, differential parameters would be more informative than the basic ones.

Actually, the values of basic parameters S2 representing the absorption of tpso-carbon atoms for three oxygen derivatives I, IIIa and IIIc (S2 = 129-130 ppm) essentially differ from other six types of compounds (VII). In the latest eight compounds the S2 parameter is distributed inside the interval S2C = 133-138 ppm without any regularity. On the contrary, for orto-carbon atoms only Sc values for benzamides VIId and VIIe (S3 ~127 ppm) are less than S3 = 128.5-132 ppm for other 6 types of compounds. The same situation takes place with the S5 parameter representing the absorption of para-carbon atoms. And there are no great differences between S4 values for all 11 compounds in the case of meta-carbon atoms.

Taking into consideration AS differential

° t-j

parameters one can see that differences between 7 types of compounds with different Z atoms have a more regular character. As it was shown previously [2, 3], the parameters AS3-4 and AS5 4 containing the most outlying from the X fragment "internal" atoms of a phenyl ring are low-informative[1]. Differential parameters AS2-3 and especially AS2 5 on the contrary are the most valuable ones because of their reliability and self-descriptiveness.

Above mentioned results show that all 7 types of compounds (VII) may again be divided into two groups. These new groups are similar by their compositions to the


Differential parameter values A8^4, ppm

A

+4.75

+2.97

+4.06

 

+6.65

+6.87

+5.74

0

+

 

+4.63

+5.11

+5.74

+5.87

+5.62

 

+7.36

+6.55

+6.07

+5.97

+6.35

 

<A

t-©

+

©

+

© ©

+

 

4 9. 0.

+

7 0.

+

2 9. 0.

+

0.

+

 

0. 2.

+

+

7 4.

1+

4 8. 0.

+

8 7. 0.

+

 

8 8. 0.

+

6 7.

1+

2 1+

4 0.

1+

0

©

1+

 

со

7

+

4 5.

©

6 4. 9.

+

 

6 4. 4.

+

©

4.

+

6.

+

6 5.

+

 

6 6.

+

4 0. 4.

+

5 4.

1+

9 0. 3.

+

7 6.

1+

 

19. 2.

+

7 0.

1+

14. 2.

+

16. 2.

+

3

-

 

 

OS

4.

+

4 7. 7.

+

0 4. 5.

+

 

5 2.

-

9 7.

-

9 2.

+

6 2. 0.

+

 

6 5. 3.

+

4 3. 0.

+

2 8. 2.

-

4 9.

-

7 3.

-

 

7 5. 3.

-

2 7. 3.

-

4 5. 2.

-

2 3. 2.

-

8

-

Basic parameter values h ppm

5

4

©

4 7.

©

6 5. 2.

 

6 2. 5.

9 0. 5.

5.

8 9.

 

3 8. 2.

3

41. 3.

3

3 5. 4.

3

5 8. 4.

3

4 5. 4.

3

 

4 9. 6.

3

4 5. 5.

3

01. 5.

3

2 9. 4.

3

5.

3

 

5

OS <n

00 <n

7 7. 7.

2

0 5.

2

 

ОС

2

2 2. 8.

2

7 7. 7.

2

8 4. 8.

2

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V Mizyuk - Рeculiarities of 13c nmr spectra of benzoylformic acid and its esters