alkanes and cycloalkanes nanoplasmonic research group organic chemistry chapter 2
TRANSCRIPT
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Alkanes and Cycloalkanes
Nanoplasmonic Research Group
Organic Chem-istry
Chapter 2
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Fully-saturated hydrocarbons: Alkanes & Cycloalkanes
Nanoplasmonic Research Group
How to READ their structures: NOMENCLATURE
Physical Properties: Interaction & Conformation
Chemical Properties: Reactions
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How to READ them ?• Systematic methods for naming compounds (IUPAC)• RULES (see page 44 middle ~ page 45)
1. Find out the longest continuous chain
2. Number the substituents
3. Write the name as one word
If 2 different chains of equal length are present, choose the one with the greater number of branch points
If the first branch points occurs at the same carbon number on both ends, begins at the end that has the second nearest branch pints
Put the substituents in alpabetical order: di-, tri-, tetra-, sec-, tert-, ignored when alphabetizing, iso-, neo- are included when alphabetizing
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How to read substituents ?
• Methyl, ethyl, propyl, etc• Iso, sec-, tert-, etc• Fluoro, chloro, bromo, iodo
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Physical Properties: Intermolecular Interaction
• Nonpolar due to the fact that C-C & C-H bonds are nearly purely covalent (no dipole moment)
• Interaction between alkanes– Induced dipole-induced dipole moment– Van der Waals attraction– M.W. dependence
• Van der Waals interaction– Permanent dipole-permanent dipole forces (Kee-
som)– Permanent dipole-induced dipole forces (Debye)– Induced dipole-induced dipole forces (London)
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Conformations of alkanes
• A consequence of rotating one car-bon atom with respect to the other carbon atom
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Conformational Energy of Ethane
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Conformational Analysis Summary
• Torsional energy– Higher energy associated with eclipsed conformation
• Torsional strain– Resistantce to rotating to an eclipsed conformation
• Steric strain– Repulsive interactions that occurs when atoms are forced
closed together than their atomic radii allow
• Gauche: spatial relationship with a 60 torsion angle• Interactions
– H-H eclipsing (torsional strain): 1.0 kcal/mol– H-Me eclipsing (mostly torsional strain) 1.4 kcal/mol– Me-Me eclipsing (steric and torsional strain) 2.6 kcal/mol– Me-Me gauche interaction (steric strain) 0.9 kcal/mol
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Why is staggered form lower in en-ergy
• Hyperconjugation– Stabilizing overlap between sigma bond
and antibonding orbitals that does not occur in the eclipsed conformer
• Electron-electron repulsion
Conformational Energy of Butane
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Naming Cyclohexane
• Find parent (ring or chain, depending on which is larger)
• Label point of attachment of alkyl, halo, etc
• Continue numbering so that the second substituent is the lowest possible number
• If 2 or more groups could potentially get the same number, use alphabetical order as a tie-breaker
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Cyclohexane
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Disubstituted Cyclohexane (I)
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Disubstituted Cyclohexane (II)
• If 2 substituents are on cyclohexane the lowest energy conformation– Has both substituents equatorial (if pos-
sible)– t-Bu is NEVER axial
• Cis-Trans Isomerism– Do not interconvert each other (see
page 59 bottom)
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The relationships of the various types of isomers