DOCSLIB.ORG

Hyperconjugation and Aromaticity- GOC

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Hyperconjugation and Aromaticity- GOC Hyperconjugation and aromaticity- GOC Why Vedantu Pro is the Best? Live Interactive Classes Test Series & Analysis ● LIVE & Interactive Teaching Style ● Exclusive Tests To Enable Practical ● Fun Visualizations, Quizzes & Application ● Mock & Subject Wise Tests, Previous Leaderboards Year Tests ● Daily Classes on patented WAVE platform ● Result Analysis To Ensure Thorough ● Dual Teacher Model For Personal Preparation Attention Assignments & Notes ● Regular Assignments To Ensure Progress ● Replays, Class Notes & Study Materials Available 24*7 ● Important Textbook Solutions What is Included in Vedantu Pro? ● Full syllabus Structured Long Term Course ● 20+ Teachers with 5+ years of experience ● Tests & Assignments with 10,000+ questions ● Option to Learn in English or Hindi ● LIVE chapter wise course for revision ● 4000+ Hours of LIVE Online Teaching ● Crash Course and Test Series before Exam Vedantu PRO-LITE FOR JEE DROPPERS 1 Month: ₹9,000 - ₹4,500/- 3 Months: ₹25,500 - ₹20,500/- 6 Months: ₹51,000 - ₹46,000/- *Link Available in Description Upto ₹5,000/- Apply Coupon Code: ABSRPRO Vedantu JEE 2021 PRO Subscription 1 Month: ₹7,500 - ₹3,750/- 3 Months: ₹21,000 - ₹16,000/- 6 Months: ₹39,000 - ₹34,000/- *Link Available in Description Upto ₹5,000/- Apply Coupon Code: ABSRPRO Vedantu JEE 2022 PRO Subscription 1 Month: ₹5,000 - ₹2,500/- 3 Months: ₹13,500 - ₹8,500/- 6 Months: ₹24,000 - ₹19,000/- 12 Months: ₹42,000 - ₹37,000/- *Link Available in Description Upto ₹5,000/- Apply Coupon Code: ABSRPRO How to Avail The Vedantu Pro Subscription 1 2 3 4 Select Your Click on Get Subscription Choose Your Subscription Apply Coupon Code Grade & Target & Click on Proceed To Pay and Make Payment *Vedantu Pro Subscription Link available in description Use the code: ABSRPRO Mesomeric effect When a group releases or withdraw orbital electron in any conjugated system then it is called M effect group and effect is known as mesomeric effect. +M group -M group Mesomeric effect Electron releasing group ー ー ー ー ー ー ー ー OH, OR, NH2 NHR, NR2 SH, SR, X etc. Mesomeric effect When a group releases or withdraw orbital electron in any conjugated system then it is called M effect group and effect is known as mesomeric effect. +M group -M group Mesomeric effect Electron withdrawing group ー ー ー ー ー ー ー ⊕ ー ⊕ NO2, CN, CHO, COR, COOH, SO3H, NR3 , NH3 , etc. Dual behaviour ーN＝O Both electron releasing as well as electron withdrawing Mesomeric effect Resonance Effect doesn’t depend upon distance unlike inductive effect Let’s solve Which of the following have -M effect (e- withdrawing mesomeric effect) ? A C = O B ㅡOH C ㅡOR D ㅡBr Let’s solve Which of the following have -M effect (e- withdrawing mesomeric effect) ? A C = O B ㅡOH C ㅡOR D ㅡBr Solution ❖ The carbonyl group contain double bonds so they can accept lone pair of electrons and thus have -M effect (electron withdrawing mesomeric effect). ❖ On the other hand ㅡOH. ㅡOR and ㅡBr have lone pair of electrons and have +M effect (electron releasing mesomeric effect). Aromatic Compounds ● Aromatic compounds are specialized cyclic compound which are known for their distinct smell. (aroma-fragrance). This group is called arenes ❖ Benzene was considered as parent aromatic compound Aromatic Compounds Huckel’s rule : Characteristics for ring being aromatic- ❖ Planarity (2-D) [sp2 carbon] ❖ Conjugated system (de-localisation of 휋 e-in ring) ❖ Cyclic ❖ Presence of (4n + 2)휋 e- in the ring. Where, (n = 0, 1, 2, 3...) Aromatic Compounds Π e- are loosely bonded electrons, lone pair are also Π e- . Aromatic Compounds ● Cyclic, Planar ● 6 e- system (4π e-’s + 2 e- from only one lone pair ) ● Follow (4n + 2) rule and 2 e-’s from LP are in complete delocalisation or in resonance ● Hence aromatic Only one lone pair is required for delocalisation Aromatic Compounds ❖ Cyclic ❖ Planar ❖ Conjugated System ❖ 4n휋 e- should present in the ring where (n = 1 2,3,...) Cyclobutadiene (n = 1 ⇒ 4휋e-) (Highly Unstable) Anti-Aromatic Compounds Some important points about Anti-Aromatic- ❖ Dimerisation Anti-Aromatic Compounds Some important points about Anti-Aromatic- ❖ Reaction with active metals Anti-Aromatic Compounds Some important points about Anti-Aromatic- ❖ Reaction with active metals Non-Aromatic Compounds Compounds which are neither aromatic nor antiaromatic. Stability order of compounds : Aromatic > non aromatic > Anti - Aromatic Let’s solve Which of the following is least stable? A B N C D O O Let’s solve Which of the following is least stable? A B N C D O O Solution O ● Cyclic ● Non-conjugated ● Non-aromatic Let’s solve Which of the following chemical system is non-aromatic ? A B C D S Let’s solve Which of the following chemical system is non-aromatic ? A B C D S Solution sp3 sp2 sp2 sp2 sp2 ● Cyclopentane-1,3-diene is a non aromatic compound ● Cyclic delocalization of electron is not possible because of the presence of sp3 hybridized carbon atom. Let’s solve Identify the following as aromatic, antiaromatic or non-aromatic: ⊕ (a) (b) S Solution ⊕ n = 1 ⇒ 4휋e- Anti-aromatic Cyclic, conjugated, planer, (4n+2) 휋e- n = 1 ⇒ 6휋 e- S Aromatic 2 e- from only one lone pair Hyperconjugation ● When a sigma CH bond of sp3 hybridised carbon is in conjugation with ힹ bond at p-orbital, half filled p-orbital or vacant p-orbital, then the bond pair e of sigma CH bond overlap with adjacent p-orbital.This phenomenon is called hyperconjugation Unshared p Orbital σ Unsaturated System Carbocation Hyperconjugation ● When a sigma CH bond of sp3 hybridised carbon is in conjugation with ힹ bond at p-orbital, half filled p-orbital or vacant p-orbital, then the bond pair e of sigma CH bond overlap with adjacent p-orbital.This phenomenon is called hyperconjugation σ Free Radicals Alpha carbon and alpha hydrogen ❖ 훼-Carbon is the carbon attached to a functional group such as C＝C. ❖ The hydrogen attached to 훼-carbon is called 훼-hydrogen. ❖ For an 훼 CーH bond to be eligible for hyperconjugation, 훼 C must be sp3 hybridized. Origin of hyperconjugation: Stability of alkene Origin of hyperconjugation: Stability of alkene ー ＝ ー ー ー ー CH3 CH CH CH3 + H2 CH3 CH2 CH2 CH3 ΔH3(expected) > ΔH2(expected) > ΔH1 But ΔH3(actual) < ΔH2(actual) < ΔH1 Origin of hyperconjugation: Stability of alkene As we increase the number of methyl groups on double bond, the stability of alkene increases Order of electron release based on inductive effect : Origin of hyperconjugation: Stability of alkene As we increase the number of methyl groups on double bond, the stability of alkene increases Order of electron donation based on hyperconjugation: ● 훼 H ↑ ● 휋 bond delocalisation ↑ ● Stability of alkene ↑ ● Heat of hydrogenation↓ Origin of hyperconjugation: Stability of alkene Mechanism of Electron Donation to explain Anomaly : No-bond resonance Baker nathan effect 휎 - 휋 effect Origin of hyperconjugation: Stability of alkene Let’s solve Mark the number of 훼-C and 훼-H in the given compounds (mark 훼-H eligible for hyperconjugation only). ＝ ー (a) CH2 CH CH3 ー ＝ ー (b) CH3 CH CH CH3 S Solution 훼 ＝ ー (a) CH2 CH CH3 훼C = 1, 훼 H = 3 훼 훼 ー ＝ ー (b) CH3 CH CH CH3 훼C = 2, 훼H = 6 Let’s solve Mark the number of 훼-C and 훼-H in the given compounds: ー ＝ ー ー (a) (CH3)2CH C(CH3) CH CH2 CH3 ー (b) CH3 CHO ー ⊕ (c) CH3 CH2 ー • (d) CH3 CH2 Solution Application of hyperconjugation ● Stability of alkenes : 흰 hydrogen ↑ hyperconjugative structure ↑ stability ↑ no-bond resonance energy ↑ ● Acidic character of alkenes : Hyperconjugation weakens the 힪 C-H bond Application of hyperconjugation Application of hyperconjugation ● Stability of carbocation : 훅⊕ H 훅⊕ 훅⊕ H C CH Positive charge on C is 2 delocalized over 훂H to give 훅⊕ stability to the carbocation. H Hyperconjugation Hybrid Application of hyperconjugation ● Stability of carbocation : Number of 훂H ⬆ Stability of carbocation ⬆ 3o 2o 1o Methyl 훂 훂 훂 훂 ( H = 9) ( H = 6) ( H = 3) ( H = 0) Let’s solve Which has more acidic 훂-H? 一 一 I. R CH2 CH=CH2 一 一 II. R CH2 CHO A I B II C Both D None Let’s solve Which has more acidic 훂-H? 一 一 I. R CH2 CH=CH2 一 一 II. R CH2 CHO A I B II C Both D None Solution In (ll), negative charge is delocalized on O while in (l), negative charge is delocalized on C. Therefore, (ll) is more stable than (l). Hence, (ll) is more acidic than (l). Let’s solve Which is more stable carbocation? ⊕ I. C(CH3)2H ⊕ II. ((CH3)2CH)3C A I B II C Both equally D None stable Let’s solve Which is more stable carbocation? ⊕ I. C(CH3)2H ⊕ II. ((CH3)2CH)3C A I B II C Both equally D None stable Solution ❖ (I) has 2훂C and 6훂H. ❖ (II) has 3훂C and 3훂H. ❖ (I) is 2o carbocation while (II) is a 3o carbocation. ❖ But since (I) has greater number of 훂H, it is more stable. Let’s solve The number of hyperconjugation structures possible in A 3 B 2 C 6 D None of these Let’s solve The number of hyperconjugation structures possible in A 3 B 2 C 6 D None of these Solution JEE MAIN 2021 CRASH COURSE ❖ Cover entire JEE Main Syllabus (as per the new pattern) with India’s Best Teachers in 90 Sessions ❖ Solve unlimited doubts with Doubt experts on our Doubt App from till Exam 8 AM to 11 PM ● 1 Batch Classes will be over in 10 Weeks ● 10 full and 10 Part syllabus test to make you exam ready ● ● Amazing tricks & tips to crack JEE Main 2021 Questions in power-packed 90 Min sessions ● ● Learn on a 2-way Interactive Platform where the teacher is always with you JEE MAIN 2021 CRASH COURSE Lightning Deal: ₹10000 ₹8000/- Batch Starts From : Every Monday *Crash Course Link Available in Description Apply Coupon Code: ABSRCC Join Vedantu JEE Telegram channel NOW! Assignments Notes Daily Update https://vdnt.in/jeepro .
Load more

Recommended publications
  • Planar Cyclopenten‐4‐Yl Cations: Highly Delocalized Π Aromatics
    Angewandte Research Articles Chemie How to cite: Angew.Chem. Int. Ed. 2020, 59,18809–18815 Carbocations International Edition: doi.org/10.1002/anie.202009644 German Edition: doi.org/10.1002/ange.202009644 Planar Cyclopenten-4-yl Cations:Highly Delocalized p Aromatics Stabilized by Hyperconjugation Samuel Nees,Thomas Kupfer,Alexander Hofmann, and Holger Braunschweig* 1 B Abstract: Theoretical studies predicted the planar cyclopenten- being energetically favored by 18.8 kcalmolÀ over 1 (MP3/ 4-yl cation to be aclassical carbocation, and the highest-energy 6-31G**).[11–13] Thebishomoaromatic structure 1B itself is + 1 isomer of C5H7 .Hence,its existence has not been verified about 6–14 kcalmolÀ lower in energy (depending on the level experimentally so far.Wewere now able to isolate two stable of theory) than the classical planar structure 1C,making the derivatives of the cyclopenten-4-yl cation by reaction of bulky cyclopenten-4-yl cation (1C)the least favorable isomer.Early R alanes Cp AlBr2 with AlBr3.Elucidation of their (electronic) solvolysis studies are consistent with these findings,with structures by X-raydiffraction and quantum chemistry studies allylic 1A being the only observable isomer, notwithstanding revealed planar geometries and strong hyperconjugation the nature of the studied cyclopenteneprecursor.[14–18] Thus, interactions primarily from the C Al s bonds to the empty p attempts to generate isomer 1C,orits homoaromatic analog À orbital of the cationic sp2 carbon center.Aclose inspection of 1B,bysolvolysis of 4-Br/OTs-cyclopentene
    [Show full text]
  • Introduction to Aromaticity
    Introduction to Aromaticity Historical Timeline:1 Spotlight on Benzene:2 th • Early 19 century chemists derive benzene formula (C6H6) and molecular mass (78). • Carbon to hydrogen ratio of 1:1 suggests high reactivity and instability. • However, benzene is fairly inert and fails to undergo reactions that characterize normal alkenes. - Benzene remains inert at room temperature. - Benzene is more resistant to catalytic hydrogenation than other alkenes. Possible (but wrong) benzene structures:3 Dewar benzene Prismane Fulvene 2,4- Hexadiyne - Rearranges to benzene at - Rearranges to - Undergoes catalytic - Undergoes catalytic room temperature. Faraday’s benzene. hydrogenation easily. hydrogenation easily - Lots of ring strain. - Lots of ring strain. - Lots of ring strain. 1 Timeline is computer-generated, compiled with information from pg. 594 of Bruice, Organic Chemistry, 4th Edition, Ch. 15.2, and from Chemistry 14C Thinkbook by Dr. Steven Hardinger, Version 4, p. 26 2 Chemistry 14C Thinkbook, p. 26 3 Images of Dewar benzene, prismane, fulvene, and 2,4-Hexadiyne taken from Chemistry 14C Thinkbook, p. 26. Kekulé’s solution: - “snake bites its own tail” (4) Problems with Kekulé’s solution: • If Kekulé’s structure were to have two chloride substituents replacing two hydrogen atoms, there should be a pair of 1,2-dichlorobenzene isomers: one isomer with single bonds separating the Cl atoms, and another with double bonds separating the Cl atoms. • These isomers were never isolated or detected. • Rapid equilibrium proposed, where isomers interconvert so quickly that they cannot be isolated or detected. • Regardless, Kekulé’s structure has C=C’s and normal alkene reactions are still expected. - But the unusual stability of benzene still unexplained.
    [Show full text]
  • On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and Its Application to Heteroatomic Π-Electron Systems
    Symmetry 2010, 2, 1485-1509; doi:10.3390/sym2031485 OPEN ACCESS symmetry ISSN 2073-8994 www.mdpi.com/journal/symmetry Article On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems Ewa D. Raczyñska 1, *, Małgorzata Hallman 1, Katarzyna Kolczyñska 2 and Tomasz M. Stêpniewski 2 1 Department of Chemistry, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 159c, 02-776 Warszawa, Poland 2 Interdisciplinary Department of Biotechnology, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 166, 02-776 Warszawa, Poland * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +48-22-59-37623; Fax: +49-22-59-37635. Received: 23 April 2010; in revised form: 19 May 2010 / Accepted: 7 July 2010 / Published: 12 July 2010 Abstract: The HOMA (Harmonic Oscillator Model of Aromaticity) index, reformulated in 1993, has been very often applied to describe π-electron delocalization for mono- and polycyclic π-electron systems. However, different measures of π-electron delocalization were employed for the CC, CX, and XY bonds, and this index seems to be inappropriate for compounds containing heteroatoms. In order to describe properly various resonance effects (σ-π hyperconjugation, n-π conjugation, π-π conjugation, and aromaticity) possible for heteroatomic π-electron systems, some modifications, based on the original HOMA idea, were proposed and tested for simple DFT structures containing C, N, and O atoms. An abbreviation HOMED was used for the modified index. Keywords: geometry-based index; π -electron delocalization; σ - π hyperconjugation; n-π conjugation; π-π conjugation; aromaticity; heteroatomic compounds; DFT 1.
    [Show full text]
  • Aromaticity Sem- Ii
    AROMATICITY SEM- II In 1931, German chemist and physicist Sir Erich Hückel proposed a theory to help determine if a planar ring molecule would have aromatic properties .This is a very popular and useful rule to identify aromaticity in monocyclic conjugated compound. According to which a planar monocyclic conjugated system having ( 4n +2) delocalised (where, n = 0, 1, 2, .....) electrons are known as aromatic compound . For example: Benzene, Naphthalene, Furan, Pyrrole etc. Criteria for Aromaticity 1) The molecule is cyclic (a ring of atoms) 2) The molecule is planar (all atoms in the molecule lie in the same plane) 3) The molecule is fully conjugated (p orbitals at every atom in the ring) 4) The molecule has 4n+2 π electrons (n=0 or any positive integer Why 4n+2π Electrons? According to Hückel's Molecular Orbital Theory, a compound is particularly stable if all of its bonding molecular orbitals are filled with paired electrons. - This is true of aromatic compounds, meaning they are quite stable. - With aromatic compounds, 2 electrons fill the lowest energy molecular orbital, and 4 electrons fill each subsequent energy level (the number of subsequent energy levels is denoted by n), leaving all bonding orbitals filled and no anti-bonding orbitals occupied. This gives a total of 4n+2π electrons. - As for example: Benzene has 6π electrons. Its first 2π electrons fill the lowest energy orbital, and it has 4π electrons remaining. These 4 fill in the orbitals of the succeeding energy level. The criteria for Antiaromaticity are as follows: 1) The molecule must be cyclic and completely conjugated 2) The molecule must be planar.
    [Show full text]
  • Aromaticity in Polyhydride Complexes of Ru, Ir, Os, and Pt† Cite This: DOI: 10.1039/C5cp04330a Elisa Jimenez-Izala and Anastassia N
    PCCP View Article Online PAPER View Journal r-Aromaticity in polyhydride complexes of Ru, Ir, Os, and Pt† Cite this: DOI: 10.1039/c5cp04330a Elisa Jimenez-Izala and Anastassia N. Alexandrova*ab Transition-metal hydrides represent a unique class of compounds, which are essential for catalysis, organic i À i À synthesis, and hydrogen storage. In this work we study IrH5(PPh3)2,(RuH5(P Pr3)2) ,(OsH5(PPr3)2) ,and À OsH4(PPhMe2)3 polyhydride complexes, inspired by the recent discovery of the s-aromatic PtZnH5 cluster À anion. The distinctive feature of these molecules is that, like in the PtZnH5 cluster, the metal is five-fold Received 23rd July 2015, coordinated in-plane, and holds additional ligands attheaxialpositions.Thisworkshowsthattheunusual Accepted 17th September 2015 coordination in these compounds indeed can be explained by s-aromaticity in the pentagonal arrangement, DOI: 10.1039/c5cp04330a stabilized by the atomic orbitals on the metal. Based on this newly elucidated bonding principle, we additionally propose a new family of polyhydrides that display a uniquely high coordination. We also report the first www.rsc.org/pccp indications of how aromaticity may impact the reactivity of these molecules. 1 Introduction many catalytic cycles, where they have either been used as catalysts or invoked as key intermediates.15,16 Aromaticity in Aromaticity is a very important concept in the contemporary general is associated with high symmetry, stability, and specific chemistry: the particular electronic structure of aromatic reactivity. Therefore, the stability of transition-metal hydride systems, where electrons are delocalized, explains their large complexes might have an important repercussion in the kinetics energetic stabilization and low reactivity.
    [Show full text]
  • Bsc Chemistry
    Subject Chemistry Paper No and Title Paper 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No and Module 3: Hyper-Conjugation Title Module Tag CHE_P1_M3 CHEMISTRY PAPER No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 3: Hyper-Conjugation TABLE OF CONTENT 1. Learning outcomes 2. Introduction 3. Hyperconjugation 4. Requirements for Hyperconjugation 5. Consequences and Applications of Hyperconjugation 6. Reverse Hyperconjugation 7. Summary CHEMISTRY PAPER No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 3: Hyper-Conjugation 1. Learning Outcomes After studying this module you shall be able to: Understand the concept of hyperconjugation. Know about the structural requirements in a molecule to show hyperconjugation. Learn about the important consequences and applications of hyperconjugation. Comprehend the concept of reverse hyperconjugation. 2. Introduction In conjugation, we have studied that the electrons move from one p orbital to other which are aligned in parallel planes. Is it possible for electron to jump from p orbital to sp3 orbital that are not parallelly aligned with one another? The answer is yes. This type of conjugation is not normal, it is extra-ordinary. Hence, the name hyper-conjugation. It is also know as no-bond resonance. Let us study more about it. 3. Hyperconjugation The normal electron releasing inductive effect (+I effect) of alkyl groups is in the following order: But it was observed by Baker and Nathan that in conjugated system, the attachment of alkyl groups reverse their capability of electron releasing. They suggested that alkyl groups are capable of releasing electrons by some process other than inductive.
    [Show full text]
  • Sc-Homoaromaticity
    This is a repository copy of Modern Valence-Bond Description of Homoaromaticity. White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/106288/ Version: Accepted Version Article: Karadakov, Peter Borislavov orcid.org/0000-0002-2673-6804 and Cooper, David L. (2016) Modern Valence-Bond Description of Homoaromaticity. Journal of Physical Chemistry A. pp. 8769-8779. ISSN 1089-5639 https://doi.org/10.1021/acs.jpca.6b09426 Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Modern Valence-Bond Description of Homoaromaticity Peter B. Karadakov; and David L. Cooper; Department of Chemistry, University of York, Heslington, York, YO10 5DD, U.K. Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K. Abstract Spin-coupled (SC) theory is used to obtain modern valence-bond (VB) descriptions of the electronic structures of local minimum and transition state geometries of three species that have been con- C sidered to exhibit homoconjugation and homoaromaticity: the homotropenylium ion, C8H9 , the C cycloheptatriene neutral ring, C7H8, and the 1,3-bishomotropenylium ion, C9H11.
    [Show full text]
  • Synthesis and Reactivity of Cyclopentadienyl Based Organometallic Compounds and Their Electrochemical and Biological Properties
    Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties Sasmita Mishra Department of Chemistry National Institute of Technology Rourkela Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties Dissertation submitted to the National Institute of Technology Rourkela In partial fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry by Sasmita Mishra (Roll Number: 511CY604) Under the supervision of Prof. Saurav Chatterjee February, 2017 Department of Chemistry National Institute of Technology Rourkela Department of Chemistry National Institute of Technology Rourkela Certificate of Examination Roll Number: 511CY604 Name: Sasmita Mishra Title of Dissertation: ''Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties We the below signed, after checking the dissertation mentioned above and the official record book(s) of the student, hereby state our approval of the dissertation submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry at National Institute of Technology Rourkela. We are satisfied with the volume, quality, correctness, and originality of the work. --------------------------- Prof. Saurav Chatterjee Principal Supervisor --------------------------- --------------------------- Prof. A. Sahoo. Prof. G. Hota Member (DSC) Member (DSC) ---------------------------
    [Show full text]
  • Structure, Stability, and Substituent Effects in Aromatic S-Nitrosothiols: the Crucial Effect of a Cascading Negative Hyperconjugation/Conjugation Interaction
    Marquette University e-Publications@Marquette Chemistry Faculty Research and Publications Chemistry, Department of 10-23-2014 Structure, Stability, and Substituent Effects in Aromatic S-Nitrosothiols: The Crucial Effect of a Cascading Negative Hyperconjugation/Conjugation Interaction Matthew Flister Marquette University, [email protected] Qadir K. Timerghazin Marquette University, [email protected] Follow this and additional works at: https://epublications.marquette.edu/chem_fac Part of the Chemistry Commons Recommended Citation Flister, Matthew and Timerghazin, Qadir K., "Structure, Stability, and Substituent Effects in Aromatic S-Nitrosothiols: The Crucial Effect of a Cascading Negative Hyperconjugation/Conjugation Interaction" (2014). Chemistry Faculty Research and Publications. 360. https://epublications.marquette.edu/chem_fac/360 Marquette University e-Publications@Marquette Chemistry Faculty Research and Publications/College of Arts and Sciences This paper is NOT THE PUBLISHED VERSION; but the author’s final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation below. Journal of Physical Chemistry : A, Vol. 18, No. 42 (October 23, 2014): 9914–9924. DOI. This article is © American Chemical Society Publications and permission has been granted for this version to appear in e-Publications@Marquette. American Chemical Society Publications does not grant permission for this article to be further copied/distributed or hosted elsewhere without the express permission from American Chemical Society Publications. Structure, Stability, and Substituent Effects in Aromatic S-Nitrosothiols: The Crucial Effect of a Cascading Negative Hyperconjugation/Conjugation Interaction Matthew Flister Department of Chemistry, Marquette University, Milwaukee, Wisconsin Qadir K. Timerghazin Department of Chemistry, Marquette University, Milwaukee, Wisconsin Abstract Aromatic S-nitrosothiols (RSNOs) are of significant interest as potential donors of nitric oxide and related biologically active molecules.
    [Show full text]
  • Contribution of Quantum Chemistry to the Study of Dienes and Polyenes
    The Chemistry of Dienes and Polyenes. Volume 1 Edited by Zvi Rappoport Copyright ¶ 1997 John Wiley & Sons, Ltd. ISBN: 0-471-96512-X CHAPTER 1 Contribution of quantum chemistry to the study of dienes and polyenes V. BRANCHADELL, M. SODUPE, A. OLIVA and J. BERTRAN´ Departament de Qu´ımica, Universitat Autonoma` de Barcelona, 08193 Bellaterra, Spain Fax: (34)35812920; e-mail: [email protected] I. INTRODUCTION ..................................... 2 II. SURVEY OF THEORETICAL METHODS .................... 2 III. GROUND STATE STRUCTURE AND VIBRATIONAL SPECTRA .... 4 A. Butadiene ........................................ 4 1. Geometry ...................................... 4 2. Vibrational frequencies and force field ................... 5 3. Conformational equilibrium .......................... 6 B. Trienes and Tetraenes ................................ 7 1. Geometries and conformations ........................ 7 2. Vibrational frequencies and force constants ................ 9 C. Longer Polyenes .................................... 9 IV. EXCITED STATES .................................... 10 A. Butadiene ........................................ 11 B. Hexatriene ........................................ 13 C. Octatetraene ...................................... 14 D. Longer Polyenes .................................... 14 V. MOLECULAR ELECTRIC PROPERTIES ..................... 15 VI. CHEMICAL REACTIVITY .............................. 17 A. The Diels Alder Reaction ............................. 17 1. Reaction mechanism ..............................
    [Show full text]
  • Effect of Hyperconjugation on Ionization Energies of Hydroxyalkyl Radicals
    J. Phys. Chem. A 2008, 112, 9965–9969 9965 Effect of Hyperconjugation on Ionization Energies of Hydroxyalkyl Radicals Boris Karpichev, Hanna Reisler, Anna I. Krylov, and Kadir Diri* Department of Chemistry, UniVersity of Southern California, Los Angeles, California 90089-0482 ReceiVed: June 14, 2008; ReVised Manuscript ReceiVed: August 01, 2008 On the basis of electronic structure calculations and molecular orbital analysis, we offer a physical explanation of the observed large decrease (0.9 eV) in ionization energies (IE) in going from hydroxymethyl to hydroxyethyl radical. The effect is attributed to hyperconjugative interactions between the σCH orbitals of the methyl group in hydroxyethyl, the singly occupied p orbital of carbon, and the lone pair p orbital of oxygen. Analyses of vertical and adiabatic IEs and hyperconjugation energies computed by the natural bond orbital (NBO) procedure reveal that the decrease is due to the destabilization of the singly occupied molecular orbital in hydroxyethyl radical as well as structural relaxation of the cation maximizing the hyperconjugative interactions. The stabilization is achieved due to the contraction of the CO and CC bonds, whereas large changes in torsional angles bear little effect on the total hyperconjugation energies and, consequently, IEs. 1. Introduction bond strengths21 and conformations20 upon substitutions, the vibrational spectra and structures of hydrocarbon radicals,22,23 Hydroxyalkyl radicals are important intermediates in combus- 1,2 the trends in electronically excited states in alkylperoxy radi- tion and atmospheric processes. The most studied of these 24 3-12 cals, and more. There is also a strong evidence that the radicals are the hydroxymethyl and 1-hydroxyethyl radicals.
    [Show full text]
  • Conjugated Molecules
    Conjugated Molecules - Conjugated molecules have alternating single and multiple (i.e. double or triple) bonds. Example 1: Nomenclature: 2,6-dimethylhepta-2,5-diene This molecule is not conjugated because it does not have alternating single and multiple bonds (the arrangement of the bonds starting from C2 is double, single, single and double). Between the two double bonds, there is a saturated center (C4) and two intersecting single bonds. Example 2: Nomenclature: 2,5-dimethylhexa-2,4-diene This molecule is conjugated because the arrangement of the bonds starting at C2 is double, single, and double. They are alternated. Example 3: Nomenclature: (2E)-hept-2-en-5-yne note: (2E) is a stereochemical identifier. The letter “E” indicates the arrangement of the double bond (where E usually refers to trans and Z refers to cis). The number “2” indicates the position of the double bond. This molecule is not conjugated because the single and multiple bonds are not alternated. Example 4: Nomenclature: (2Z)-hex-2-en-4-yne This molecule is conjugated because there is an alternation of multiple and single bonds (double, single, and triple starting from C2). More examples: note: the term conjugation refers to parts of the molecule. If you can find one conjugated system within the molecule, that molecule is said to be conjugated. Example: In this molecule, the double bond A is not conjugated. However, since double bond B is conjugated with double bond C, the molecule is said to be conjugated. Special Nomenclature: The Letter "S" stands for “single” and indicates that we are talking about the conjugated double bonds.
    [Show full text]