organic chemistry chapter 1
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Organic Chemistry Chapter 1. Bonding and Isomerism. Nanoplasmonic Research Group. Organic Chemistry. How would you explain “Organic Chemistry” to your ~ ? - PowerPoint PPT PresentationTRANSCRIPT
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Bonding and Isomerism
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Organic Chem-istry
Chapter 1
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Organic Chemistry
• How would you explain “Organic Chemistry” to your ~ ?
• The scientific study of the structure, properties, composition, reac-tions, and syntheses (preparation of chemical compounds that contain carbon)
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Organic Chemistry is Rational and Sys-tematic !!!
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Why & How we study Organic Chemistry ?
• Why– Pervasive in nature– Chemical foundation of biology– Improve standard of living (medicine,
plastics,…)
• How– Examine structure and analyze how it
governs reactivity
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Background Review: Atom
• Nucleus + Electrons• Nucleus consists of Protons and Neu-
trons except H• Atomic Number = # of Protons• Atomic Weight = # of Protons + # of
Neutrons (Electrons are comparably light)
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Electron Configuration and Valence Electrons
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Electron redistribution (change in configuration) is the origin of chemical change
WHY? Attain lower ENERGY
Process of chemical bonding:Adding or taking away outer shell elec-
trons to gain a closed shell configuration
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Ionic vs. Covalent Bonding
• Ionic bonding –Why NaCl can be easily dis-
solved in water at Room Tem-perature even if it has a high melting point ?
• Covalent bonding– Bonding Energy: Energy stored
in the bond– Bond length
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Basic Chemistry of Carbon
• Features– Four valence electrons– Neither to gain four electrons to be C4-nor
lose all to be C4+– Tend to share all electrons to make eight
valence electrons around it
• Polar covalent bond arises due to the different electronegativities of atoms Please refer to Table
1.4
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Valence and Isomerism
• Valence– Number of bonds that an atom of the el-
ement can form
• Isomerism– A molecular formula can’t give an infor-
mation about how atoms in the structure are arranged, but a STRUCTURAL FOR-MULA CAN!!!
– Isomers: The same numbers and kinds of atoms but DIFFERENT arrangement
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Formal Charge
• How to calculate– FC = number of valence electrons of the
atom in isolation – lone pair electrons on this atom in the molecule – half the total number of electrons participating in co-valent bonds with this atom in the mole-cule
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Resonance (I)
• Pls take a look at the carbonate ion
• Resonance structure– Identical arrangement of atoms but different ar-
rangement of electrons
• How to arrange ALL ELECTRONS (valence elec-trons in the structure + borrowed electrons from somewhere
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Resonance (II)
• The basic principles– Keep the relative positions of all the compo-
nent atoms the same– The same number of paired and unpaired
electrons
• Evaluating contribution– The number of covalent bonds in a structure– Formal charge separation– Electronegativity of charge bearing atomes
and charge density
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Why we have to care about Reso-nance ??
Lots of chemical reactions occur because of the attraction of one molecule containing a region of high electron density to a second
molecule containing a region of low electron density
+ -
To predict how and when two molecule will react, need to be able to predict the regions
of low and high electron density
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Molecular Orbital Theory
• Atomic Orbitals: Unhybridized orbitals on an atom (s, p, d)
• Linear Combination of Atomic Orbitals (LCAO): Individual wave functions (or-bitals) combine to form hybrid atomic or-bitals and molecular orbitals
• Hybrid Atomic Orbitals: Combination of atomic orbitlas from the same atom
• Molecular Orbitals: Combination of atomic orbitals from different atoms
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Shapes of Orbitals
Spherical or Dumbbell-like
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How to combine each other (sigma bond)
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How to combine each other (pi bond)
Any differences between two ???
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If all bonding occurred between simple s- and p- orbitals, then all
bond angles would be ca. 90o
• Valence Shell Electron-Pair Repulsion (VSPER) theory
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Point is “Electrons repel each
other”
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Thanks to Lewis..but
• Lewis theory of chemical bonding– Electron-dot structure– Limited in explaining the 3-D geometries
of molecules
• The orbital view of bonding– Valence Shell Electron-Pair Repulsion
(VSPER) theory– Hybridization
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Please take a look at Figure 1.10
• How would you think about this in terms of orbitals ??????
Hybridization came out!!!
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Let’s classify organic molecules (I)
• With respect to Molecular Framework
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Does it have only chains of carbon atoms ?
Acyclic compounds
Heterocyclic compounds Carbocyclic compounds
Does it have heteroatoms in the ring ?
YES NO
NOYES
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• With respect to Functional group– Please refer to Table 1.2 & Lecture Mate-
rials
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Let’s classify organic molecules (II)