Organic Chemistry I- chapter 4

-are aliphatic hydrocarbons having only C-C and C-H sigma bonds
-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: acyclic alkanes
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-contain carbons joined in one or more rings
-have the molecular formula CnH2n
-have two fewer H atoms than an acyclic alkane with the same number of carbons
alkanes: cycloalkanes
-methane: CH4
-ethane: CH3CH3
-both sp3 hybridized and tetrahedral(109.5degrees)
structures for the two simplest alkanes
-a three-carbon alkane
-imply any three-dimensional arrangement
lewis structrues are not meant to…
-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
euivalent representations
-just one of the two ways to arrange four carbon atoms(structural isomers)
-straight-chain or normal alkane(n-alkane)
-branched-chain alkane
-the atoms are connected to each other
constitutional isomers differ in the way…
-each having molecular formula C5H12
how many constitutional isomers are there for pentane?
-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
carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bound to them
-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…
hydrogen atoms are classified as primary, secondary, tertiary depending on…
-a CH2 group
methylene group
-a group of compounds that differ by only a CH2 group/methylene group
homologous series
-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
straight chain alkanes
-have molecular formula CnH2n and contain carbon atoms arranged in a ring
-by adding the prefix cylco-(name of acyclic alkane having the same number of carbons)
how are simple cycloalkanes names
-a caustic compounds isolated from certain ants
-comes from latin word formic>ant
formic acid
-pungent principle of garlic
-derived from botanical name for garlic
-international union of pure and applied chemistry
IUPAC system of nomenclature
most drugs have three names since IUPAC can be long and complex
-follows the accepted rules of nomelclature and indicates the compound’s chemical structure; this is the IUPAC name
systematic name of a drug
-the official, internationally approved name for the drug
generic name of a drug
-is assigned by the company that manufactures it
-catchy and often easy to remember
trade name of a drug
-parent name
the three parts to naming every organic molecules
-indicated the number of carbons in the longest continuous carbon chain in the molecule
parent name
-indicates what functional group is present
-reveals the identity, location and number of substituents attached to the carbon chain
the parent name for one carbon is…
the parent name for two carbons is
-carbon substituents bonded to a long carbon chain
-formed by removing one hydrogen from an alkane
alkyl groups
-change the -ane ending of the parent alkane to -yl
-methane becomes methyl(CH3-)
-ethane becomes ethyl(CH3CH2-)
to name an alkyl group…
-denotes a general carbon group bonded to a functional group
-thus, denotes an alkyl group
-propyl(with alkyl group)
removal of each of these H atoms forms a different alkyl group with a different name…
-there are four possible alkyl groups containing four carbon atoms, each having a different name
-butyl, sec-butyl, isobutyl, and tert-butyl
because there are two different butane isomers to begin with, each having two different kinds of H atoms…
-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
first step needed to name an alkane
-number of atoms in the carbon chain
–number the longest chain to give to first substituent the lower number
–if the first substituent is the same distance from both ends, number the chain to give the second substituent the lower number. always look for the first point of difference in numbering from each end of the longest chain
–when numbering a carbon chain results in the same numbers from either end of the chain, assign the lower number alphabetically to the first substituent
second 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, …
third step needed to name an alkane
-combine substituent names and numbers + parent + suffix
–precede the name of the parent by the names of the substituents
-alphabetize the name of the substituents, ignoring all prefixes except iso, as isopropyl and isobutyl
-precede the name of each substituent by the number that indicates its location. there must be ONE NUMBER FOR EACH SUBSTITUENT
-separate numbers by commas and separate numbers from letters by hyphens. the name of an alkane is a single word, with no spaces after hyphens or commas
fourth step needed to name an alkane
-name the parent (nonane)
-number the parent chain (first substituent)
-name and number the substituents (tert-butyl)
-combine parts
quick steps solution (1-4)
-the prefic cyclo- immediately precedes the name of the parent
cycloalkanes are names by using similar rules, but…
-fine the parent cycloalkane
–count the number of carbon atoms in the ring and use the parent name for that number of carbons. add the prefic cyclo- and the suffix -ane to the parent name
-name and number the substituents
–no number is needed to indicate the location of a single substituent
–for rings with more than one substituent, begin numbering at one substituent and proceed around the ring clockwise or counterclockwise to give the second substituent the lower number
—with two different substituents, number the ring to assign the lower number to the substituents alphabetically
steps to naming cycloalkanes
-if the number of carbons in the ring is greater than or equal to the number of carbons in the longest chain, the compound is named as a cycloalkane
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?
butyl, sec-butyl, isobutyl, tert-butyl
-organic compounds identified by a name that does not follow the IUPAC system of nomenclature
common names
-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
-largely composed of methane
-lesser amounts of ethane, propane, and butane
-burn in the presence of oxygen, releasing energy for cooking and heating
natural gas
-a complex mixture of compounds, most of which are hydrocarbons containing 1-40 carbon atoms
-a process that separates into usable fractions that differ in boiling point
-diesel fuel
some different types of fuels
-petroleum is an example of a nonrenewable type of fuel
-C-C and C-H bonds, and as a result they exhibit only weak van der Waals forces
alkanes contain only nonpolar…
-the three-dimensional structure of molecules
-carbon-carbon sigma bonds
-conformations occur during rotations allowing Hs on one carbon to adopt different orientations relative to the hydrogens on the other carbon
rotation occurs around…
-polar compounds of comparable size
-increasing strength of intermolecular forces> increasing boiling point
alkanes have low bp’s compared to more…
-increases because of increased surface area
bp increases as the number of carbons…
-of decreased surface area
the bp of isomers decreases with branching because…
-polar compounds of comparable size
-increasing strength of intermolecular forces> increasing boiling point
alkanes have low mp’s compared to more…
-increase because of the increased surface area
mp increases as the number of carbons…
mp increases with increased…
-are soluble in organic solvents
-are insoluble in water
solubility and alkanes
-different arrangement of atoms that are interconverted by rotation about single bonds
-eclipsed conformation
-staggered conformation
two different types of conformations
-the C-H bonds on one carbon are directly aligned with C-H bonds on the adjacent carbon
eclipsed conformation
-the C-H bonds on one carbon BISECT the H-C-H bond angle on the adjacent carbon
staggered conformation
-60 degrees converts an eclipsed conformation into a staggered conformation, and vice versa
rotating the atoms on one carbon by…
-the angle that separates a bond on one atom from a bond on an adjacent atom
dihedral angle
-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
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
steps to draw a newman projection
can staggered and eclipsed conformations be draw in 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
with newman projection…
-eclipsed conformation
-less stable(staggered conformation is most stable, minimum energy)
-torsional strain
which type on conformation has increased energy?
-an increase in energy caused by eclipsing interactions
torsional strain
-60 degree, when rotation has reached eclipsed conformation
maximum energy increased at what degree
-intermediate in energy
conformations that are neither staggered nor eclipsed are…
-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
to analyze the different conformations that result from rotation…
a staggered conformation with two larger groups 180 degrees from each other is called…
a staggered conformation with two larger groups 60 degrees from each other is called…
-an increase in energy resulting when atoms are forced too close to one another
steric strain
-gauche, because of steric strain
are gauche conformations or anti conformations generally higher in energy?
staggered conformations are at energy minima and eclipsed conformations are at energy…
-increase energy
unfavorable steric interactions…
-the energy difference between the lowest and highest energy conformations
barrier to rotation
-staggered and anti
a zigzag arraangement of carbons keeps them…
-an increase in energy when tetrahedral bond angles deviate from the optimum angle of 109.5 degrees
angle strain
-they are not flat
-somewhat puckered
how to cycloalkanes reduce strain where there are more tha three carbon atoms present?
-the most common ring size in naturally occurring compounds
-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)
the chair conformation
-three C atoms pucker down, alternating around the ring. these C atoms are called up C’s and down C’s
in a cyclohexane, thee C atoms pucker up and…
each carbon in cyclohexane has two different kinds of hydrogens
-are located above and below the ring(along the perpendicular axis)
axial hydrogens
-are located in the plane of the ring(around the equator)
equatorial hydrogens
-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
how to draw a chair form of cyclohexane
cyclohexane does not remain in a single…
-an important conformational change, which can be viewed as a two-step process
-a down carbon flips up>boat
-the orignial carbon can flip downm reforming the initial conformation
-or the second up carbon can flip down>second cahri conformation
two possible ways boat form can flip
-up carbons become down carbons and the down carbons become the up carbonds
because of ring-flipping…
-interconverted during a ring flip
-axial H atoms become equatorial H atoms, and equatorial H atoms become axial H atoms
axial and equatorial H atoms are…
-the two hydrogens at either end of the boat that are forced close to each other
flagpole hydrogens
-larger substituents are more stable in the equatorial position
the equatorial position has more room than the axial position, so…
-eclipsing interactions between Hs cause torsional strain
-the proximity of the flagpole Hs cause steric strain
the boat form of cyclohexane is less stable than the chair forms for two reasons:
-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
how to draw the two conformations for a substituted cyclohexane
-same side of the ring- either below or above- during the process of ring-flipping
a substituent always stays on the …
-equally stable
two conformations of methylcyclohexane are different, so they are not…
-unfavorable 1,3-diaxial interactions, destablizing a cyclohexane conformation
larger axial substituents create…
-so, a group on one side of the ring can never rotate to the other side of the ring
-large substituents>equatorial axis
is rotation about the C-C bonds in a ring restricted?
-isomers that differ only in the way the atoms are oriented in space
-cis isomer has two groups on the same side of the ring
-trans isomer has two groups on opposite sides of the ring
cis and strans are used to distinguish these stereoisomers
-it is lower in energy
if a conformation has both larger substituent groups in the roomier equatorial position..
-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-)
procedure used to analyze the relative stability of two conformations of any distributed cyclohexane

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