Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (https://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
https://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (https://www.sciepub.com)

Label_Title

Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (https://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
https://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (https://www.sciepub.com)

Label_Title

Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (https://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
https://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (https://www.sciepub.com)

Application of Hammett and Taft Equations Together on the Deprotonation Equilibriums of Isoxazolium Cations: A One Hour Graduate Classroom Teaching

Sanjeev Rachuru, Raju Manthena, K. Ankamma, D. A. Padmavathi, V. Jagannadham*

Department of Chemistry, Osmania University, Hyderabad-500007, India

Abstract: Hammett and Taft equations are applied together on the deprotonation equilibriums of isoxazolium cations.

Keywords: Hammett equation, Taft equation, Isoxazolium cations

Received November 26, 2023; Revised December 28, 2023; Accepted January 04, 2024

Citation: Sanjeev Rachuru, Raju Manthena, K. Ankamma, D. A. Padmavathi, V. Jagannadham, Application of Hammett and Taft Equations Together on the Deprotonation Equilibriums of Isoxazolium Cations: A One Hour Graduate Classroom Teaching. World Journal of Chemical Education, 12 (1). 1-5. January 2024. doi:10.12691/wjce-12-1-1

1. Introduction

Use of Hammett equation [1-4] dealing with meta and para-substituted benzene derivatives and Taft equation [5,6] dealing with ortho-substituted benzene derivatives in elucidating the reaction mechanisms in Physical-Organic Chemistry is indubitable. Since their introduction [1-6] numerous publications have appeared in literature [3,4] and are still being published to date. Application of Hammett and Taft equations to five membered aromatic heterocyclic ring systems was less commonly studied. The first application of Hammett law (not as an equation) [7] to furan ring was with 5-X-2-furoic acids [9]. But this was quoted in reference [10] as it was published in 1935 [11] even before the Hammett equation came into existence. In reference [10] by Freeman it is surprising to see even a Hammett ρ value was reported for the dissociation of 5-X-2-furoic acids without knowing Hammett σ values because evaluation of Hammett σ values took place only in 1937 [1]. Despite numerous research works on the application of Hammett and Taft equations to several organic reactions appeared in literature, their application to five membered ring systems did not find much place in chemistry research [9,12] except a one-page small publication appeared 50 years ago [10] and references cited therein. In this publication [10] the information of substituents in furan and thiophene derivatives used did not find a place. We have recently reported the application of Linear Free Energy Relationships (LFER) to the N(1)-H acidities of five membered nitrogen heterocyclic ring systems [13]. In the present work we have taken up the application of Hammett and Taft equations to deprotonation equilibriums of isoxazolium cations.

2. Methods

Linear correlation of pKaH versus (Hammett σ + Taft σ*) is done using the KaleidaGraph software, Reading, PA, USA. The chemical structures are drawn using ChemDraw software. Individual Hammett (σ) and Taft (σ*) substituent constants are from different sources [1-8]. The pKaH values of isoxazolium cations are from reference [14]. Wherever the Taft σ* values are not available, they are calculated using the equation σ, where σm is the meta-substituent constant of that substituent [15]. And they were used in the summation of the Hammett and Taft substituent constants (column 3 and 4 in Table 1).

3. Results and Discussion

Visual observation of benzene and five membered heterocycles to look for the similarity of para, meta and ortho-carbons of benzene and 5th, 4th, and 3rd carbons of five membered 5 or 4- or 3-(X)-2-(Y)-heterocycles (as an example isoxazole with Z = O and V = N in the scheme 2 below for structure C):

As shown in scheme 1, it is known that all the six carbon atoms in the benzene ring are sp2 hybridized and benzene is a planar hexagon molecule.

Scheme 1

Scheme 2

This explains an equal possibility for the formation of C1 - C2, C3 - C4, C5 - C6 π bonds or C2 - C3, C4 - C5, C6 - C1 π bonds. The hybrid structure is represented by inserting a circle in the ring as shown above in scheme 1. Hence, it explains the formation of two resonance structures proposed by Kekule [16] and they will always be in dynamic equilibrium. At any given point of time during the dynamic equilibrium process of benzene, the statistical percentage of existence of either A or B in scheme 2 is 50:50.

Now comparing the structure, A or B and the structure of the 5-X-2-Y-heterocycle C1 of scheme 2, the functional group Y and the substituent X are separated by one single bond and two double bonds or simply by two pairs of π-electrons or by two sp2 carbons in benzene ring B and the heterocycle C1. Therefore, it can be assumed that the substituent electronic effects can be transmitted from carbon 4 bearing the substituent X to the functional group Y at carbon 1 of the benzene. This kind of situation of the structure C1 where in the substituent electronic effects can be transmitted from carbon 5 bearing the substituent X to the functional group Y at carbon 2 of the heterocycle would be just like that of structure A or B. Therefore carbon 5 of the structure C1 of scheme 2 could best be assumed as a para-carbon. The transmittance of substituent effect from carbon 5 to the deprotonation site (=HN⁺-) via oxygen is also likely, for reasons, though the hybridization of oxygen is in between sp2 and sp3 having lot more towards sp3 because the bond angle of ∠CON was reported as 108.8 determined by microwave spectroscopy and it is not much away from 109.5, the tetrahedral angle [17]. There is a very recent review article on hybridization which narrates nicely the relation between bond angle index and the quantity spm hybridization character [18]. And the angle of ∠CON of 108.8 which is little less than the typical tetrahedral angle of 109.5 led to evaluate the hybridization of oxygen and it gave a small fraction of sp2 character, due to this the transmittance of substituent effect via oxygen cannot completely be ruled out as shown in structure C2 of scheme 2.

Similarly, now comparing the structure E and the structure of the 4-X-2-Y-heterocycle F1 of scheme 3, the functional group Y and the substituent X are separated by one single bond and one double bond or simply by a pair of π-electrons or by one sp2 carbon. It can be assumed that the substituent electronic effects can be transmitted from carbon 3 bearing the substituent X to the functional group Y at carbon 1 of the benzene. This kind of situation of the structure F1 where in the substituent electronic effects can be transmitted from carbon 4 bearing the substituent X to the functional group Y at carbon 2 of the heterocycle would be just like that of structure E. Therefore, the carbon 4 of the structure F1 could best be assumed as a meta-carbon. Also, like above the transmittance of substituent effect via oxygen cannot completely be ruled out as shown in structure F2 of scheme 3.

Again, similarly the carbon 3 of the structure I could best be assumed as an ortho-carbon as shown in scheme 4.

Scheme 3

Scheme 4

In fact, molecular orbital calculations, and dipole moment data of 2-X-thiophene carboxylic acids suggested that the para, meta and ortho carbons of benzene correspond to 5, 4 and 3 carbons of the 5 membered heterocycle [19,20]. From the correlation of carbon-13 chemical shifts versus 1H-proton chemical shifts, in which the striking parallelism of the resonance shifts of the benzene and five membered heterocycle nuclei, implies that the resonances of both nuclei respond in a parallel way to the local π-electron density on the carbon atom [21]. And as such five membered heterocycles with one or two heteroatoms are planar pentagons. They have sp2 hybridized carbon atoms. They possess significant aromatic character resulting from the lone pair of electrons of the hetero atom/s and the two pairs of carbon π electrons.

Now applying the above said observations to isoxazolium cations: The substituents are assumed at position 3 as ortho-substituents, at position 4 as meta-substituents and at position 5 as para-substituents. And for disubstituted and trisubstituted isoxazoles the corresponding summed-up [(Hammett σ + Taft σ*)] values are taken. Reasonably a good straight line is obtained (Figure 1). Though the correlation coefficient is a little poor (R = 0.8074), the trend is unmistakable. And another striking and important explanation for a little poor correlation of Hammett-Taft plot is: Isoxazole is aromatic but not as aromatic as benzene. The lone pair of oxygen does not participate effectively in resonance because oxygen being more electronegative. As a result, the isoxazole ring cannot maintain an effective uninterrupted delocalization of its π-electrons to have a continuous conjugation like that in benzene.

And the substituents are assumed at position 3 as ortho-substituents as above, at position 4 as para-substituents and at position 5 as meta-substituents for the transmittance via oxygen. Figure 2 is the Hammett-Taft plot for the transmittance via oxygen. And for both types of transmittance the corresponding substituent constants are calculated and are given in column 3 and 4 respectively of Table 1.

4. Conclusions

The slopes i. e. the ρHammett-Taft = -1.32 and -1.43 from the plots should be read as positive value since the plots are made pKaH versus (Hammett σ + Taft σ*) substituent constants. The positive ρHammett-Taft values indicate that electron withdrawing substituents increase the deprotonation and electron donating substituents decrease the deprotonation.

Table 1. (Hammett σ + Taft σ*) values and pKaH data of isoxazolium cations

Figure 1. Plot of pkaH vs (Hammett σ + Taft σ*)

Figure 2. Plot of pkaH vs (Hammett σ + Taft σ*)

The Hammett-Taft plots are shown in figures 1 and 2.

The authors don’t have any conflict of interest.

References

[1]   | L. P. Hammett., J. Am. Chem. Soc., vol. 59, page 96 (1937).
[2]   | L. P. Hammett., "Physical Organic Chemistry." McGraw Hill Book Co., Inc., New York, 1940, P. 184.
[3]   | H. H. Jaffe, Chem. Rev., 53, 191 (1953).
[4]   | P. R. Wells, Chem. Rev., 63, 171 (1963).
[5]   | R. W. Taft, J. Am. Chem. Soc., 74, 2729 and 3120 (1952).
[6]   | R. W. Taft, J. Am. Chem. Soc. 75, 4538, (1953).
[7]   | L. P. Hammett, Chem. Rev., vol. 17, 125, (1935).
[8]   | Corwin Hansch, A. Leo, and R. W. Taft, Chem. Rev., 91, 165-195 (199l).
[9]   | Imoto, E. and Motoyama, R., Bull. Naniwa Univ., Series A. 2. 127 (1954).
[10]   | F. Freeman, J. Chem. Edn., vol. 47, 140, (1970).
[11]   | W. E. Catlin, Iowa State Coll. J. Sci.,10, 65 (1935).
[12]   | Salo Gronowitz, Thiophene and its derivatives part 2 in The Chemistry of Heterocyclic Compounds, an Interscience publication, 1986 by John Wiley & sons, Inc.
[13]   | R. Sanjeev and V. Jagannadham, Current Physical Chemistry (Bentham Science), vol. 12, page 117-127, (2022).
[14]   | “The Chemistry of Heterocyclic Compounds”, by Grünanger Paolo, An Interscience publication, 1991, John Wiley & Sons. Page 114.
[15]   | “Lange's Handbook of Chemistry”, by John A. Dean, Fifteenth Edition McGraw-Hill, Inc., New York, Copyright renewed 1972 by Norbert Adolph Lange, please go directly to Section 9 to look for the equation.
[16]   | A. Kekulé, Justus Liebigs Ann. Der Chemie, Vol. 162, page 77-124, (1872), https://en.wikipedia.org/wiki/Benzene#cite_note-18.
[17]   | E. Schaumann, Science of Synthesis, Volume 11: Category 2, Hetarenes and Related Ring Systems, 2002.
[18]   | Guy Lamoureux and John F. Ogilvie, Journal of Chemical Reviews, Vol. 4, issue 2, pages 120-146, (2022).
[19]   | L. Melander, Ark. Kemi, 11, 397 (1957).
[20]   | Ram Keswani and Henry Freis, J. Am. Chem. Soc., 71, I789 (1949).
[21]   | (a) H. Spiesecke and W. G. Schneider, J. Chem. Phys., 35, 731 (1961), (b) Tetrahedron Letters, 468, (1961).