Organic Chemistry Chapter 3

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organic chemistry
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the chemistry of carbon on planet earth, all accessible carbon is processed through living organisms
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carbon cycle
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all available planetary carbon is processed as “organic” carbon over and over
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other important elements in organic chemistry
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Li,Na, K, Mg, N, Ca, P, O, S, Cl, Br, I
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what’s the big deal about carbon chemistry?
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-there are <16 million known organic compounds(majority of compounds) -there are in theory an infinite number of organic compounds -new organic compounds of desired structure are created every day by: -chemisits/biochemists -organisms
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why is carbon chemistry pervasive?
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-carbon forms covalent bonds with itself using single, double, and triple bonds -carbon forms covalent and/or ionic bonds with >90 elements (no noble gases or highly radioactive elements)
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hydrocarbons
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compounds containing only Carbon and Hydrogen
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universal alkane formula
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CnH(2n+2) n=number of carbons 2n+2=number of hydrogens
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rule of four
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in stable organic molecules, all carbons have four bonds Carbon attached to 4 atoms is always sp3 hybridized-tetrahedral geometry
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constitutional isomerism
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molecules that have the same formula, but different atom-atom connection different compounds therefore have different physical properties
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Naming an alkene
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1.) identify the longest chain of carbons 2.) number the chain from 1,2…n such that carbon 1 is assigned to the beginning of the chain and the first branch is minimized 3.) name the alkyl groups and assign their locations using your numbering system
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Isobutane
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2-methylpropane=IUPAC
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Acetylene
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Ethyne=IUPAC
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1* primary carbon
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Carbon attached to one other carbon
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2* secondary carbon
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Carbon attached to 2 other carbons
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3* tertiary carbon
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Carbon attached to 3 other carbons
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4* quaternary carbon
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Carbon attached to 4 other carbons
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1* primary hydrogen
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Hydrogen attached to 1* carbon
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2* secondary hydrogen
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Hydrogen attached to 2* carbon
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3* tertiary hydrogen
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Hydrogen attached to 3* carbon
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General cycloalkane formula
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CnH2n
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Conformations of alkanes
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Conformations are structures that interconvert by rotation about carbon-carbon single bonds Any 3-D arrangement of atoms in a molecule that results by rotation about a single bond Equivalent term: “conformational isomers” Carbon-carbon single bonds tend to rotate(twist) freely and rapidly
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Staggered conformation
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a conformation about a carbon to carbon single bond in which the atoms on one carbon are as far apart as possible from the adjacent carbon More stable than eclipsed conformation
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Torsion strain
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Inherent instability caused by eclipsing arises when atoms separated by 3 bonds are forced from a staggered conformation to an eclipsed conformation
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Cis-trans isomers
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isomers that have the same order of attachment of their atoms, but a different arrangement of their atoms in space, due to the presence of either a ring or a carbon-carbon double bond Cis-trans isomers do not interconnect They are not constitutional isomers (same atom to atom conductivity) They are constitutionally identical have an arrangement of atoms that cant be interchanged by rotation about a sigma bond under ordinary conditions
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Cis isomers
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Have 2 substituents on the same side of the plane
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Trans isomers
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Have 2 substituents on the opposite sides of the plane
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Axial bonds
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bond on a chair conformation of a cyclohexane ring that extends from ring parallel to imaginary axis of ring Straight up and down 3 bonds point up, other three point down if axial bond on carbon points upward, equatorial bond on that carbon points slightly downward
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Equatorial bonds
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bond on chair conformation of cyclohexane ring that extends from the ring roughly perpendicular to the imaginary axis of ring Directed outward alternate:1st slightly up and then slightly down Substituents larger than H prefer to be equatorial Bigger substituent group should be equatorial in order to be favored
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Physical properties of alkanes
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-nonpolar -soluble in most organic solvents, insoluble in water -boiling points increase with increasing molecular weight -when comparing constitutional isomers, the boiling point decreases with greater chain branching–more branched structures=boils at a lower temperature
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Role of dispersion forces for liquid alkanes
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Alignment of induced dipoles causes adjacent molecules to stick together Round or branched alkanes do not align efficiently so they stick together less…smaller area of contact. Therefore lower boiling point
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Combustion reaction of an alkane
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CnH(2n+2)+((3n+1)/2)O2 –> nCO2+(n+1)H2O All C become CO2 All H become H2O
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Line angle formula
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Each line ending represents a carbon atom and a line represents a bond A carbon at every bend and at every end
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Alkyl group
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Group derived by removing a hydrogen from an alkane Given the symbol -R
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Iso
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For names beyond propane, iso indicates the one end of an otherwise unbranched chain terminates in a (CH3)2CH group
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Cycloalkane
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Saturated hydrocarbon that contains carbon atoms joined to form a ring Contains two fewer hydrogen atoms than an alkane with the same number of carbon atoms
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IUPAC system of nomenclature
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1. Prefix: number carbon atoms in parent chain 2. Infix: nature of C-C bonds in parent chain -an: all single bonds -en: one or more double bonds -yn: one or more triple bonds 3. Suffix: class of compound to which substance belongs -e: hydrocarbon -ol: alcohol -al: aldehyde -one: ketone -olc acid: carboxylic acid
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eclipsed conformation
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a conformation about a C-C single bond in which the atoms on one carbon are as close as possible to the atoms on the adjacent carbon
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angle strain
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strain that arises when a bond angle is either compressed or expanded compared with its optimal value
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chair conformation
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most stable puckered conformation of a cyclohexane ring; all bond angles are about 109.5* and bonds to all adjacent carbons are staggered -99.9% of all cyclohexanes are in the chair conformation
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boat conformation
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a puckered conformation of a cyclohexane ring in which carbons 1 and 4 of the ring are bent toward each other -less stable than chair conformation -torsional strain is created by 4 sets of eclipsed hydrogen interactions and steric strain created by one set of flagpole interactions
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steric strain
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strain that arises when atoms separated by 4 or more bonds are forced abnormally close to one another(forced closer than their atomic radii allow)
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chemical property of alkanes and cycloalkanes
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interness quite unreactive toward most reagents(nonpolar and only sigma bonds) will react with O2(combustion)
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major sources of alkanes
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fossil fuels (natural gas, petroleum, coal)

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