Pub Date : 2020-07-30DOI: 10.26434/chemrxiv.12734039
V. Yadav
The collinearity of terminal p orbitals of a diene with that of a dienophile is required for an effective overlap to result in s bond formation during the Diels-Alder reaction. The ease of the DA reaction of a cyclic diene with a given dienophile, therefore, must also depend on the distance between the termini of the diene. A distance larger than the unsaturated bond of the dienophile is expected to raise the energy of activation. This scenario has been amply demonstrated from the study of reactions of several dienes, some designed to serve the purpose, with different dienophiles. The five-ring heterocycles pyrrole, furan, thiophene and selenophene possess varying aromatic character for the varied resonance participation of the heteroatom lone pair with ring p bonds. The aromaticity decreases in the same order due to: (a) the increasing sC-X (X = heteroatom) bond length lifts the bond uniformity required for ring current, hence aromaticity, such as in benzene and (b) size-mismatch of the interacting lone pair orbital and the ring p orbitals, especially in thiophene and selenophene, both allowing poor overlap in the ground state structures. It is demonstrated that increase alone in the activation energies of the DA reactions of pyrrole, furan, thiophene and selenophene cannot be considered a measure of relative aromaticity as often done and even theoretically attempted in many ways to prove just that. The separation of the termini of the diene has a much larger role in the determination of activation energy, especially in thiophene and selenophene, than their aromaticity profile. There cannot be a measure better than the relative intensity of heteroatom lone pair overlap with ring p bonds, giving rise to a six-electron like system in following Hückel’s 4n+2 rule, to assess the relative aromaticity.
{"title":"A Computational Study of the Relative Aromaticity of Pyrrole, Furan, Thiophene and Selenophene, and Their Diels-Alder Stereoselectivity","authors":"V. Yadav","doi":"10.26434/chemrxiv.12734039","DOIUrl":"https://doi.org/10.26434/chemrxiv.12734039","url":null,"abstract":"The collinearity of terminal p\u0000orbitals of a diene with that of a dienophile is required for an effective\u0000overlap to result in s bond formation during the Diels-Alder reaction.\u0000The ease of the DA reaction of a cyclic diene with a given dienophile,\u0000therefore, must also depend on the distance between the termini of the diene. A\u0000distance larger than the unsaturated bond of the dienophile is expected to\u0000raise the energy of activation. This scenario has been amply demonstrated from\u0000the study of reactions of several dienes, some designed to serve the purpose,\u0000with different dienophiles. The five-ring heterocycles pyrrole, furan,\u0000thiophene and selenophene possess varying aromatic character for the varied resonance\u0000participation of the heteroatom lone pair with ring p bonds. The aromaticity\u0000decreases in the same order due to: (a) the increasing sC-X (X = heteroatom) bond\u0000length lifts the bond uniformity required for ring current, hence aromaticity, such\u0000as in benzene and (b) size-mismatch of the interacting lone pair orbital and\u0000the ring p orbitals, especially in\u0000thiophene and selenophene, both allowing poor overlap in the ground state\u0000structures. It is demonstrated that increase alone in the activation energies\u0000of the DA reactions of pyrrole, furan, thiophene and selenophene cannot be considered\u0000a measure of relative aromaticity as often done and even theoretically attempted\u0000in many ways to prove just that. The separation of the termini of the diene has\u0000a much larger role in the determination of activation energy, especially in\u0000thiophene and selenophene, than their aromaticity profile. There cannot be a\u0000measure better than the relative intensity of heteroatom lone pair overlap with\u0000ring p bonds, giving rise to a six-electron like\u0000system in following Hückel’s 4n+2 rule, to assess the relative aromaticity.","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129639990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-06-07DOI: 10.1007/978-981-10-1139-9
V. Yadav
{"title":"Steric and Stereoelectronic Effects in Organic Chemistry","authors":"V. Yadav","doi":"10.1007/978-981-10-1139-9","DOIUrl":"https://doi.org/10.1007/978-981-10-1139-9","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129437579","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-981-10-1139-9_3
V. Yadav
{"title":"Diastereoselectivity in Organic Reactions","authors":"V. Yadav","doi":"10.1007/978-981-10-1139-9_3","DOIUrl":"https://doi.org/10.1007/978-981-10-1139-9_3","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121699446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-3-030-75622-2_1
V. Yadav
{"title":"Steric and Stereoelectronic Control of Molecular Structures and Organic Reactions","authors":"V. Yadav","doi":"10.1007/978-3-030-75622-2_1","DOIUrl":"https://doi.org/10.1007/978-3-030-75622-2_1","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133227652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-3-030-75622-2_6
V. Yadav
{"title":"The Overlap Component of the Stereoelectronic Effect vis-à-vis the Conservation of Orbital Symmetry Rules","authors":"V. Yadav","doi":"10.1007/978-3-030-75622-2_6","DOIUrl":"https://doi.org/10.1007/978-3-030-75622-2_6","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"105 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124868683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-3-030-75622-2
V. Yadav
{"title":"Steric and Stereoelectronic Effects in Organic Chemistry","authors":"V. Yadav","doi":"10.1007/978-3-030-75622-2","DOIUrl":"https://doi.org/10.1007/978-3-030-75622-2","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122640977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-3-030-75622-2_5
V. Yadav
{"title":"The Conservation of Orbital Symmetry Rules (Woodward–Hoffmann Rules)","authors":"V. Yadav","doi":"10.1007/978-3-030-75622-2_5","DOIUrl":"https://doi.org/10.1007/978-3-030-75622-2_5","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128958874","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-3-030-75622-2_2
V. Yadav
{"title":"Reactions on Saturated and Unsaturated Carbons","authors":"V. Yadav","doi":"10.1007/978-3-030-75622-2_2","DOIUrl":"https://doi.org/10.1007/978-3-030-75622-2_2","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114664739","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1007/978-981-10-1139-9_4
V. Yadav
{"title":"A(1,2) and A(1,3) Strains","authors":"V. Yadav","doi":"10.1007/978-981-10-1139-9_4","DOIUrl":"https://doi.org/10.1007/978-981-10-1139-9_4","url":null,"abstract":"","PeriodicalId":447840,"journal":{"name":"Steric and Stereoelectronic Effects in Organic Chemistry","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121073745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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