Lecture 2
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This document summarizes key concepts from a lecture on organic chemistry including: - The learning objectives are to understand hydrocarbons, bonding types, conjugation and stability of conjugated systems. - Important terms defined include ionic bonding, covalent bonding, sigma and pi bonds. - Organic compounds contain carbon and play important roles in living organisms and industrial applications. They typically have low melting/boiling points and solubility in water but flammability. - Hydrocarbons are classified as saturated, alkenes and alkynes based on their level of saturation. Conjugation occurs through overlapping p-orbitals across sigma bonds to delocalize pi electrons. Conjugated systems are more stable than isolated
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This presentation describes the concept of Hyperconjugation in simple words, gives definition of hyperconjugation, explains why it is called as 'No bond Resonance' and gives the effects of hyperconjugation on the chemical properties of compounds: alkyl cations and their relative stability, alkyl radicals and their relative stability, alkenes and their relative stability, bond length, anomeric effect and Baker - Nathan effect.
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Contributed by: Samuel Redstone (Undergraduate), University of Utah, 2016
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Hyperconjugation occurs when a σ bond and adjacent π bond become involved in resonance. This delocalization stabilizes molecules like carbocations, free radicals, alkenes, and alkynes. Specifically, hyperconjugation in carbocations involves overlap between the carbocation's empty p-orbital and the σ orbitals of alpha hydrogens. In free radicals, it is the overlap between the odd electron's p-orbital and the σ orbital of an alkyl group. For alkenes and alkynes, stability arises from partial overlap between sp3 σ orbitals and the π orbitals of the multiple bonds. This document discusses the hyperconjugation resonance structure effects in different organic molecules.
Hyperconjugation
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This document discusses isomers and organic compound structure. It begins by explaining that organic molecules can be described at different structural levels, from molecular formula to configuration. Compounds with the same molecular formula but different connectivity are called constitutional isomers. It also discusses condensed and bond-line structural formulas as shortcuts. The document goes on to cover resonance structures and how delocalized electrons lead to resonance hybrids rather than fixed structures. It concludes by discussing molecular geometries based on valence shell electron pair repulsion theory and how to determine a molecule's dipole moment from its structure.
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This document provides an overview of organic chemistry concepts including:
- The origin of organic chemistry as the study of compounds from living organisms.
- The role of carbon in organic compounds and their importance to human biology.
- Principles of atomic structure including electron shells and orbitals.
- Bond formation through sharing or transferring electrons to attain stable configurations.
- Drawing Lewis structures and accounting for formal charges and resonance.
- Molecular geometry from hybrid atomic orbitals and how this relates to bond angles.
- Intermolecular forces between molecules and various effects that influence molecular properties.
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This document discusses structural theory in organic chemistry. It covers topics like bond fission and its types (homolysis and heterolysis), organic reagents (electrophiles, nucleophiles, free radicals), types of organic reactions (substitution, elimination, addition, rearrangement), inductive effect and its applications, and mesomeric effect and its applications. Examples are provided to illustrate key concepts. Essay and short answer questions are also included at the end to test understanding of topics covered.
4 converted (1)
This document provides an introduction to hydrocarbons, which are organic compounds composed of hydrogen and carbon. It discusses the characteristics of hydrocarbons and defines different types including aliphatic hydrocarbons (alkanes, alkenes, alkynes), aromatic hydrocarbons, and introduces chemical bonding concepts like ionic bonds, covalent bonds, and coordinate covalent bonds. It provides examples and properties of different hydrocarbon groups and bond types.
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Introduction on forces of supra molecular chemistry, host-guest, synthetic supra molecules, enantioselective molecular recognition and chiral hosts.
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This document provides an introduction to organic reactions for medical students. It defines key terms like electrophiles, nucleophiles, and reaction mechanisms. The main categories of organic reactions - addition, elimination, substitution, and rearrangement - are outlined. Examples are given of each reaction type. Curly arrows are introduced to show the movement of electron pairs in reaction mechanisms. The roles of electrophiles and nucleophiles are explained, and homolytic and heterolytic bond cleavage are defined.
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1. The document discusses organic chemistry, which involves the study of carbon-containing compounds. It covers topics such as classification of organic molecules, structural representation, functional groups, and reaction types.
2. Organic compounds are classified as aliphatic, heterocyclic, and homocyclic compounds. Structural formulas are used to represent organic molecules, including complete, condensed, and bond line formulas.
3. Functional groups determine properties of organic compounds. Reaction types covered include substitution, addition, elimination, and rearrangement reactions.
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Lecture 2
- 1. Lecture 2 Dr. Moona Mehboob Khan 17.1.2013 1
- 2. Learning Objectives Students will able to understand basic concept of the following Hydrocarbons Bonding Conjugation Types of conjugation Stability characters of conjugated system 2
- 3. Atom Important Terms Bonding Ionic Covalent Co-ordinate covalent Dipole moments Sigma bond Pi-bond 3
- 4. Organic Chemistry Study of carbon containing compounds except few as carbon di oxide ,carbon mono oxide ,carbonates ,bicarbonates,cyanates ,thiocynates etc. Organic compounds play important role in our life as in food (protein ,carbohydrates ,fats) , ,medicine, pesticides ,harmones , steroids ,enzymes ,vitamins ,antiseptics,dyes etc 4
- 5. Properties of Organic compounds They have low melting and boiling point, low solubility in water but high in nonpolar solvents ,flammable ,nonconductor of electricity. They exhibit covalent bonding and isomerism ,have slow chemical reaction. 5
- 6. Hydrocarbons Saturated Alkayne CnH2n+2 Unsaturates Alkene CnH2n & Alkyne CnH2n-2 6
- 7. Bonding 7
- 8. Chemical Bonding Bonding Ionic Covalent Co-ordinate covalent Dipole moments Sigma bond Pi-bond Sigma bonding orbital Pi-bonding orbital 8
- 9. Single bonds are always sigma bonds. Multiple bonds consist of a combination of sigma and pi bonds: double: one sigma bond, one pi bond triple: one sigma bond, two pi bonds In order to form a pi bond, there must be at least one unhybridized p orbital on each of the two atoms Bonds can also form due to overlap between unhybridized p orbitals oriented perpendicular to the internuclear axis In these p (pi) bonds, the electron density is concentrated symmetrically above and below the internuclear axis 9
- 10. Ionization potential Electron affinity Bond Energy (The energy required to break the bond in a molecule is called bond energy which arises due to attractive forces between the atoms.) Bond length (The distance between the two bonded atoms is called bond length.This is due to attraction and repulsion forces of atoms.) Electronegativity of an atom is a measure of it’s power to attract electron in a covalent bond. 10
- 11. Polar Bonds When a covalent bond is formed between two atoms with different electronegativities the more electronegative atom will acquire a partial negative charge and the less electronegative atom will acquire a positive charge .Such a bond having a negative and positive end is said to be a polar bond. 11
- 12. Non-polar Bonds When a covalent bond is formed between two atoms with same electronegativities (C-C, H-H, F-F ), the electrons involved in the bond are shared equally. There is no positive and negative end such a bond is said to be a non-polar bond. 12
- 13. Cyclic Structure The molecules which consists of carbon atoms joined to form close rings. These are called cylic compounds or ring structure e.g cyclohexane, benzene. 13
- 14. Conjugation Conjugation is the overlap of one p-orbital with another across an intervening sigma bond A conjugated system is a system of connected porbitals with delocalized electrons in compounds with alternating single and multiple bonds. This system have a p-orbital on an atom adjacent to double bond-molecules with delocalized pi bonds. The compound may be cyclic, linear or mixed. 14
- 15. Types Isolated / non conjugated; C=C-C-C=C Conjugated ; C=C-C=C Cumulated ; C=C=C 15
- 16. Conjugation Allyl radical CH2=CH-CH3 + X2----Low temp----- CH2X-CHX- CH3 (addition reaction) But when temperature is high & concentration of halogen is low then CH2=CH-CH3 + X2------- CH2=CH-CH2X + HX (Substitution reaction) This is allylic hydrogen atom & substitution is allylic substitution 16
- 17. Stability of conjugated system Conjugated Carbonyls: α,β-unsaturated systems containing conjugated double bonds, not just those of dienes, are more stable than those containing unconjugated double bonds. O O 2-Cyclohexenone (more stable) 3-Cyclohexenone (less stable) 17
- 18. Hyperconjugation The interaction of the electrons in a sigma bond (usually C–H or C–C) with an adjacent empty (or partially filled) non-bonding p-orbital to give an extended molecular orbital that increases the stability of the system It is also known as sigma-pi conjugation no bond resonance. It is a permanent effect. 18
- 19. References Organic chemistry by IL Finar Organic chemistry by Solomons & Fryhle Organic chemistry by Brown Foote Inversion 19