alkanes
-are aliphatic hydrocarbons having only C-C and C-H sigma bonds
alkanes: acyclic alkanes
-have the molecular formula CnH2n+2 where n=an integer
-also called saturated hydrocarbons because they have the maximum number of hydrogen atoms per carbon
alkanes: cycloalkanes
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structures for the two simplest alkanes
-methane: CH4
-ethane: CH3CH3
-both sp3 hybridized and tetrahedral(109.5degrees)
propane
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lewis structrues are not meant to...
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euivalent representations
-if you follow the carbon chain from one end to the other, you move across the same three carbon atoms in both representations
-the bends in a carbon chain don't matter when it comes to identifying different compounds
butane
-CH3CH2CH2CH3(C4H10)
-just one of the two ways to arrange four carbon atoms(structural isomers)
-straight-chain or normal alkane(n-alkane)
isobutane
-C4H10
-branched-chain alkane
constitutional isomers differ in the way...
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how many constitutional isomers are there for pentane?
-three
-each having molecular formula C5H12
carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bound to them
-a primary carbon(1 degree carbon) is bonded to one other C atom
-a secondary carbon(2 degree carbon) is bonded to two other C atoms
-tertiary...
-quaternary...
hydrogen atoms are classified as primary, secondary, tertiary depending on...
-the type of carbon atom to which they are bonded
-a primary hydrogen(1 degree) is on a C bonded to one other C atom
-a secondary...
-a tertiary...
methylene group
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homologous series
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straight chain alkanes
-CH4 methane, no isomers
-C2H6 ethane, no isomer
-C3H8 propane, no isomers
-C4H10 butane, 2 isomers
-C5H12 pentane, 3 isomers
-C6H14 hexane, 5 isomers
-C7H16 heptane, 9 isomers
-C8H18 octane, 18 isomers
-C9H20 nonane, 35 isomers
-C10H22 decane, 75 isomers
-C20H42 eicosane, 366,319 isomers
cycloalkanes
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how are simple cycloalkanes names
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formic acid
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allicin
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IUPAC system of nomenclature
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most drugs have three names since IUPAC can be long and complex
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systematic name of a drug
-follows the accepted rules of nomelclature and indicates the compound's chemical structure; this is the IUPAC name
generic name of a drug
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trade name of a drug
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the three parts to naming every organic molecules
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parent name
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suffix
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prefix
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the parent name for one carbon is...
-meth-
the parent name for two carbons is
-eth-
alkyl groups
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to name an alkyl group...
-change the -ane ending of the parent alkane to -yl
-methane becomes methyl(CH3-)
-ethane becomes ethyl(CH3CH2-)
R
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removal of each of these H atoms forms a different alkyl group with a different name...
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because there are two different butane isomers to begin with, each having two different kinds of H atoms...
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first step needed to name an alkane
-sometimes only C atoms will be drawn, in which case each has enough H atoms to make it tetravalent
-find the parent carbon chain and add the suffix( -ane for each alkane)
--if more than one chain has same longest length(bends don't matter), chose the one with more substituents
second step needed to name an alkane
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third step needed to name an alkane
-name and number the substituents
--name the substituents as alkyl groups, and use the numbers from step 2 to designate their location
--every carbon belongs to either the longest chain or a substituent, but not both
--each substituent needs its own number
-if two or more identical substituents are bonded to the longest chain, use prefixes to indicate how many: di, tri, tetra, ...
-"dimethyl
fourth step needed to name an alkane
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quick steps solution (1-4)
-name the parent (nonane)
-number the parent chain (first substituent)
-name and number the substituents (tert-butyl)
-combine parts
cycloalkanes are names by using similar rules, but...
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steps to naming cycloalkanes
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when an alkane is composed of both a ring and a long chain, what determines whether a compound is named as an acyclic alkane or cycloalkane?
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butyl, sec-butyl, isobutyl, tert-butyl
...
common names
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dodecahedrane
-a beautifully symmetrical compound composed of 12 five-membered rings, is one molecule that goes by its common name
common names for some polycyclic alkanes
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natural gas
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petroleum
-a complex mixture of compounds, most of which are hydrocarbons containing 1-40 carbon atoms
refining
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some different types of fuels
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nonrenewable
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alkanes contain only nonpolar...
-C-C and C-H bonds, and as a result they exhibit only weak van der Waals forces
stereochemistry
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rotation occurs around...
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alkanes have low bp's compared to more...
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bp increases as the number of carbons...
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the bp of isomers decreases with branching because...
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alkanes have low mp's compared to more...
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mp increases as the number of carbons...
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mp increases with increased...
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solubility and alkanes
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conformations
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two different types of conformations
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eclipsed conformation
-the C-H bonds on one carbon are directly aligned with C-H bonds on the adjacent carbon
staggered conformation
-the C-H bonds on one carbon BISECT the H-C-H bond angle on the adjacent carbon
rotating the atoms on one carbon by...
-60 degrees converts an eclipsed conformation into a staggered conformation, and vice versa
dihedral angle
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newman projection
-a graphic that shows the three groups bonded to each carbon atom in a particular C-C bond, as well as the dihedral angle that separates them
steps to draw a newman projection
-look directly down the C-C bond (end-on), and draw a circle with a dot in the center to represent the carbons of the C-C bond
-draw in the bonds
-add the atoms on each bond
can staggered and eclipsed conformations be draw in newman projection?
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with newman projection...
-always consider one C-C bond only and draw the atoms bonded to the carbon atoms, NOT the carbon atoms in the bond itself
which type on conformation has increased energy?
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torsional strain
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maximum energy increased at what degree
-60 degree, when rotation has reached eclipsed conformation
conformations that are neither staggered nor eclipsed are...
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to analyze the different conformations that result from rotation...
-rotate one carbon atom in 60 degree increments either clockwise or counterclockwise, while keeping the other carbon fixed. continue until you return to the original conformation
a staggered conformation with two larger groups 180 degrees from each other is called...
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a staggered conformation with two larger groups 60 degrees from each other is called...
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steric strain
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are gauche conformations or anti conformations generally higher in energy?
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staggered conformations are at energy minima and eclipsed conformations are at energy...
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unfavorable steric interactions...
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barrier to rotation
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a zigzag arraangement of carbons keeps them...
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angle strain
-an increase in energy when tetrahedral bond angles deviate from the optimum angle of 109.5 degrees
how to cycloalkanes reduce strain where there are more tha three carbon atoms present?
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cyclohexane
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the chair conformation
-cyclohexanes adopt this puckered conformation which is more stable than any other possible conformation
-all C-C-C bond angles are 109.5 degrees(eliminates angle strain and torsional strain)
in a cyclohexane, thee C atoms pucker up and...
-three C atoms pucker down, alternating around the ring. these C atoms are called up C's and down C's
each carbon in cyclohexane has two different kinds of hydrogens
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axial hydrogens
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equatorial hydrogens
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how to draw a chair form of cyclohexane
-draw the carbon skeleton
--draw three parts of the chair: a wedge, a set of parallel lines, and another wedge
--then join them together
--the bottom 3 C's come out of the page, and for this reason, bonds to them are often highlighted in bold
-label the up C's and down C's on the ring
--there are 3 up and 3 down C's, and they alternate around the ring
-draw in the axial H atoms
--on an up C the axial H is up
--on a down C the axial H is down
-draw in the equatorial H atoms
--the axial H is down on a down C, so the equatorial H must be up
--the axial H is up on an up C, so the equatorial H must be down
cyclohexane does not remain in a single...
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ring-flipping
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two possible ways boat form can flip
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because of ring-flipping...
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axial and equatorial H atoms are...
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flagpole hydrogens
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the equatorial position has more room than the axial position, so...
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the boat form of cyclohexane is less stable than the chair forms for two reasons:
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how to draw the two conformations for a substituted cyclohexane
-draw one chair dorm and add the substituents
--arbitrarily pick a ring carbon, classify it as an up or down carbon, and draw the bonds. each C has one axial and one equatorial bond
--add the substituents, in this case H and CH3, arbitrarily placing one axial and one equatorial
--this forms one of the two possible chair conformations, labeled conformation 1
-ring-flip the cyclohexane ring
--convert up Cs to down Cs and vice versa. the chosen up C now puckers down
-add the substituents to the second conformation
--draw axial and equatorial bonds. on a down C the axial bond is down
--ring-flipping converts axial bonds to equatorial bonds, and vice versa. the equatorial methyl becomes axial
--this forms the other possible chair conformation, labeled conformation 2
a substituent always stays on the ...
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two conformations of methylcyclohexane are different, so they are not...
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larger axial substituents create...
-unfavorable 1,3-diaxial interactions, destablizing a cyclohexane conformation
is rotation about the C-C bonds in a ring restricted?
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stereoisomers
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cis and strans are used to distinguish these stereoisomers
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if a conformation has both larger substituent groups in the roomier equatorial position..
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procedure used to analyze the relative stability of two conformations of any distributed cyclohexane
-a cis isomer has two substituents on the same side, either both up bonds or both down bonds
-a trans isomer has two substituents on opposite sides, on up and one down
-whether substituents are axial or equatorial depends on the relative location of the two substituents(on carbons 1,2-, 1,3-, or 1,4-)