Aromatic electrophilic substitution reactions
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1. Spectroscopy involves using electromagnetic radiation to obtain information about atoms and molecules. Infrared (IR) spectroscopy specifically analyzes molecular vibrations that occur when IR radiation is absorbed.
2. IR spectroscopy is useful for structure elucidation and identification of organic compounds by determining their functional groups based on characteristic absorption bands. It can also be used to study reaction progress and detect impurities.
3. Factors like hydrogen bonding, coupling effects, and electronic effects can influence vibrational frequencies observed in IR spectra. Advanced applications include quantitative analysis, studying isomerism, and determining unknown contaminants.
Resonance----(Oganic)
Resonance structures represent different arrangements of electrons in a molecule that have the same positions of nuclei but different bonding patterns. Resonance contributes to the stability of molecules like benzene by delocalizing electrons across multiple equivalent structures. The actual structure of a molecule represented by resonance is a hybrid of the contributing structures, with bond lengths intermediate between single and double bonds. Delocalization of electrons is depicted using curved arrows between resonance structures.
RESONANCE.pptx
Resonance structures represent different arrangements of electrons in a molecule that have the same arrangement of nuclei. They are hypothetical structures that contribute to the true structure, which is a hybrid of all resonance forms. Benzene is an example where the true structure is an average of different Kekule and Dewar structures, giving each C-C bond equal length and bond order of 1.5. Resonance increases stability by delocalizing electrons over the whole molecule.
Molecular orbital theory (conjugated molecules)
Bonding and Antibonding interactions; Idea about σ, σ*, π, π *, n – MOs; HOMO, LUMO and SOMO; Energy levels of π MOs of different conjugated acyclic and cyclic systems; Hückel’s rules for aromaticity; Frost diagram
Electronic.ppt
This document discusses electronic spectroscopy techniques such as ultraviolet-visible (UV-vis) spectroscopy and chiroptical spectroscopy. It describes how UV-vis spectroscopy can be used to study electronic transitions in molecules, detect functional groups, and perform quantitative analysis. Chiroptical spectroscopy techniques like circular dichroism and optical rotary dispersion are used to determine stereochemistry by measuring differences in absorption of left and right circularly polarized light. Selection rules and origins of electronic transitions are also summarized.
Electronic Spectroscopy.ppt
This document discusses electronic spectroscopy techniques such as ultraviolet-visible (UV-vis) spectroscopy and chiroptical spectroscopy. It describes how UV-vis spectroscopy can be used to study electronic transitions in molecules, detect functional groups, and perform quantitative analysis. The fundamentals of UV-vis spectroscopy, including electronic transitions, selection rules, solvent effects, and absorption intensity are summarized. Chiroptical spectroscopy techniques like circular dichroism and optical rotary dispersion are also introduced.
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一.毕业证【q微741003700】成绩单、使馆认证、教育部认证、雅思托福成绩单、学生卡等！
二.真实使馆公证(即留学回国人员证明,不成功不收费)
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◇在校期间，因各种原因未能顺利毕业……拿不到官方毕业证【q/微741003700】
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◇不清楚认证流程以及材料该如何准备；
◇回国时间很长，忘记办理；
◇回国马上就要找工作，办给用人单位看；
◇企事业单位必须要求办理的
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◇申请留学生创业基金
留信网认证的作用:
1:该专业认证可证明留学生真实身份
2:同时对留学生所学专业登记给予评定
3:国家专业人才认证中心颁发入库证书
4:这个认证书并且可以归档倒地方
5:凡事获得留信网入网的信息将会逐步更新到个人身份内，将在公安局网内查询个人身份证信息后，同步读取人才网入库信息
6:个人职称评审加20分
7:个人信誉贷款加10分
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With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
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Aromatic electrophilic substitution reactions
- 1. AROMATIC ELECTROPHILIC SUBSTITUTION REACTIONS CECH-202 UNIT-3(A) By - Ms MAYURI R SOMPURA
- 2. INTRODUCTION By - Ms MAYURI R SOMPURA reactions Non-polar (free radical) addition substitution polar electrophilic nucleophilic
- 3. SOURCE OF ELECTRONS – BENZENE By - Ms MAYURI R SOMPURA • Every carbon atom of benzene is 𝑠𝑝2 hybridized. • Each carbon posses a set of three 𝑠𝑝2 hybrid orbitals. • They are used to form two sigma bonds with neighboring carbons and one to form sigma bond with hydrogen. • Every carbon has one unhybridised 2𝑝𝑧 orbital occupying one electron. • This orbital is perpendicular to the plane of benzene ring.
- 4. SOURCE OF ELECTRONS – BENZENE By - Ms MAYURI R SOMPURA • All these six orbitals overlap with each other to form a new molecular orbital. • These molecular orbitals are not fixed to one carbon atom. • They keep on circulating in the molecular orbital and are responsible for formation of additional 𝜋 bond between carbon atoms. • Hence, they are known as delocalized 𝜋 electrons. • These are also responsible for aromaticity of benzene.
- 5. SOURCE OF ELECTRONS – BENZENE By - Ms MAYURI R SOMPURA • By presence of 6 𝜋 electrons:- Benzene behaves as lewis base Source of electrons to attract electrophile Undergoes SE (substituted electrophilic) reactions
- 6. MONO - SUBSTITUTION IN BENZENE By - Ms MAYURI R SOMPURA
- 7. DEFINITION OF SE REACTIONS By - Ms MAYURI R SOMPURA • The replacement of an atom or a group attached to carbon of benzene nucleus, by another group is known as aromatic substitution. • If the incoming group is an electrophile, then it is known as electrophilic aromatic substitution reaction.
- 8. MONO - SUBSTITUTION IN BENZENE By - Ms MAYURI R SOMPURA • All six hydrogens of benzene are identical, hence when one H atom is replaced only one product is obtained.
- 9. MONO - SUBSTITUTION IN BENZENE By - Ms MAYURI R SOMPURA
- 10. GENERAL MECHANISM OF SE REACTION By - Ms MAYURI R SOMPURA • Suppose reagent is EZ. • This furnishes electrophile E+ and remaining part Z- acts as nucleophile. • Mechanism has two steps:- 1. Attack by E+ upon benzene to form stable benzenonium ion (carbocation type) 2. Abstraction of H+ from benzenonium by Z- to from product Ph-E.
- 11. GENERAL MECHANISM OF SE REACTION By - Ms MAYURI R SOMPURA 1. Generalization of necessary electrophile.
- 12. GENERAL MECHANISM OF SE REACTION By - Ms MAYURI R SOMPURA 2. Attack from electrophile onto benzene. • This is a slow step reaction. • Hence, rate determining step.
- 13. GENERAL MECHANISM OF SE REACTION By - Ms MAYURI R SOMPURA 3. Resonance :- positive charge is dispersed all over the ring which results into a stable speices.
- 14. GENERAL MECHANISM OF SE REACTION By - Ms MAYURI R SOMPURA 4. Abstraction of H+: • This is a fast reaction & it gives final product.
- 15. ENERGY PROFILE GRAPH By - Ms MAYURI R SOMPURA
- 16. EVIDENCE By - Ms MAYURI R SOMPURA • Kinetics :- ➢Rate determining step involves two molecules – benzene and reagent; so it is an bimolecular electrophilic substitution reaction. • Spectroscopy :- ➢The existence of E+, Z- & benzonium ion has been proved by spectroscopy. ➢( nuclear magnetic resonance spectroscopy and infra red spectro)
- 17. ASSIGNMENT By - Ms MAYURI R SOMPURA What is an electrophile ? What is a nucleophile ? What is electromeric effect ? How will you define substitution reactions ? Define – electrophilic substitution reactions How can we consider benzene as a source of electrons ? What is the general mechanism of SE reactions ? Give mono substituted reactions of benzene. Draw energy profile graph discussing general electrophilic substitution reactions