CHEM 301: Ch2 Structure and Properties of Organic Molecules
65 Cards in this Set
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bond length
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internuclear distance where attraction and repulsion are balanced
(which also gives minimum energy)
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Sigma bond
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most electron density centered along the line connecting nuclei
aka cylindrically symmetrical bond
most common bonds in organic compounds
ALL SINGLE BONDS IN ORGANIC COMPOUNDS ARE THIS BOND, EVERY DOUBLE OR TRIPLE BOND CONTAINS ONE OF THESE BONDS
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Sigma* antibonding molecular orbital
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orbitals overlap out of phase
2 1s wave functions have opposite signs so they tend to cancel out where they overlap, resulting in a node separating two nuclei
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Pi bond
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results from overlap of two P orbitals oriented perpendicular to line connecting nuclei
overlap is parallel not linear
DOUBLE BOND
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sp Hybrid orbitals
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bonding of s and p orbitals on the same aton
electron denisty concentrated on one side of orbital
results in a pair of directional hybrid orbitals pointed in opposite directions
bond angle of 280 degrees, linear bonding arrangement
180 deg,LINEAR
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sp2 orbitals
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orienting three bonds as far apart as possible
120 degree bond angles, trigonal geometry
results in three hybrid orbitals
remaining p orbital perpendicular to plane of three hybrid orbitals
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sp3 hybrid orbitals
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four bonds oriented as far apart as possible
tetrahedron 109.5 degree bond angles
1s and 3 ps
ex) methane
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Determining hybridization of orbital
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number of hybrid orbitals on an atom = number of sigma bonds + number of lone pairs on the atom
find widest possible separation of for bonds and lone pairs
first bond is sigma, second and third is pi
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conformations
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structures differing only in rotations about a single bond
not including rigid double bonds
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eclipsed conformation
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C-H bonds are parallel, like mirror image
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staggered conformation
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diagonal mirror image of bonds
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cis molecule
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methyl groups "on same side of the double bond, either both on top or both on bottom
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trans molecule
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methyl groups on opposite sides
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isomers
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different compounds with same molecular formula
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constitutional isomers
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aka structural isomers
differ only in bonding sequence
atoms are connected differently
may differ in position of double bond or other group by having a ring or other feature
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cis-trans isomers
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aka geometric isomers
differ in the geometry of the groups on a double bond
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stereoisomers
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isomers that only differ in how their atoms are oriented in space
atoms bonded in same order
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bond dipole moments
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polarity of an individual bond
(mu=amount of charge x distance between charges)
units of debye
can be used to calculate bond lengths and charge separations
range from 0 (symmetrical bonds) to 3.6D (strongly polar triple bond)
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1 Debye
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unit of dipole moment
3.34 x 10^-30
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molecular dipole moment
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dipole moment of molecule as a whole
value is equal to vector sum of all individual bond dipole moments
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dipole-dipole forces
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attractive intermolecular forces resulting from the attraction of the positive and negative ends of the dipole moments of polar molecules
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london dispersion forces
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principal attractive force in nonpolar molecules
one of the van der waals forces
arises from temporary dipole moments
last fraction of a second
larger surface are = higher boiling points due to these foces
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affects on surface area
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the more branches, the more spherical, weaker forces, lower boiling points
vice versa
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hydrogen bonding
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technically strong dipole-dipole attraction
only when hydrogen is bonded to N, O, or F (organic compounds do not contain F)
the more bonds the higher boiling point
alcohols form stronger bonds than amines in these bonds (probably because oxygen is more electronegative)
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polar solute in polar solvent
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dissolves
process of hydration in sodium chloride
h2o molecules strongly polar and release energy when bonds are broken, enough energy to disrupt lattice of salt and allow it to dissolve
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polar solute in nonpolar solvent
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does not dissolve
nonpolar molecules in solvent cannot solvate strongly and do not overcome lattice energy of salt crystal
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nonpolar solute in nonpolar solvent
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dissolves
molecules of nonpolar substance are weakly attracted to eachother, van der waals attractions in solute easily overcome by those in solvent
large increase in entropy despite little change in energy
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nonpolar solute in polar solvent
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does not dissolve
nonpolar molecules weakly attracted to eachother - little energy required to separate them
polar molecules strongly attracted to eachother
decrease in entropy
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hydrocarbons
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compounds composed entirely of hydrogen and carbon
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alkane
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type of hydrocarbon
contains only single bonds
-ane suffix
first part of name indicates the number of carbon atoms `
main components of heating gases
have no functional group
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Naming alkanes + ane
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prefix (number of carbons)
meth
eth
prop
but
pent
hex
hept
oct
non
dec
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cycloalkanes
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alkanes in the form of a ring
cyclo + prefix (number of carbons) + ane
to draw use prefix to draw number of lines in the shape of a ring
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functional group
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part of molecule where reactions usually occur
double bonds, hydroxyl groups, halogen atoms
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alkyl groups
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alkane portion of a molecule
one hydrogen bond removed to to allow bonding to the rest of the molecule
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naming alkyl groups
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treat larger fragment as parent compound, smaller compound alkyl group
add -yl
ex- ethyl attached to cyclohexane (ethylcyclohexane)
R also represents alkyl group (or other unreactive group - alkylcyclopentane
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alkenes
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hydrocarbons that contain carbon-carbon double bonds
carbon-carbon double bond is most reactive part, aka the functional group
-ene suffix
prefix/number of carbons.. meth eth, prop,but,pent.. (if more than one double bond chain labeled and lowest number is listed)
ex) but-…
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naming alkenes
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if more than one double bond, chain is numbered and lower number indicates position
prefix/number of carbons.. meth eth, prop,but,pent.. (if more than one double bond chain labeled and lowest number is listed)
ex) but-1-ene (double bond is located on the first carbon of the 4)
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cis-trans isomerism in alkenes
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double bonds cannot rotate
add cis if symmetrical, add trans if diagonal
cis/trans + prefix + number +ene
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alkynes
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hydrocarbons with carbon carbon triple bond
triple bond is functional group
-yne suffix (there are exceptions)
triple bond is linear (no cis-trans)
same as naming alkynes, number chain, add prefix for number of carbons and number where triple bond is present
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cycloalkynes
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rare
four colinear atoms not easily bent into ring
only stable if ring is large, 8 or more carbons
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aromatic hydrocarbons
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aka arenese
may look like cycloalkenes
different properties
derivatives of benzene
6 membered ring with three double bonds
stable represented by Ar
when benzene is substituent, it is a phenyl group called Ph
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alcohols
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organic compounds that contain hydroxyl group (-OH) as their functional group
most common/polar organic compounds because hydroxyl is strongly polar and can hydrogen bond
-ol suffix
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ethers
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two alkyl groups bonded over Oxygen atom
much more polar than hydrocarbons
cannot hydrogen bond with themselves
named by name of alkyl group and word ether
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aldehydes and ketones
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C=O bond is functional group
carbonal group strongly polar
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ketone
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two alkyl groups bonded to carbonyl group
-one suffix
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aldehyde
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one alkyl group and one hydrogen bonded to carbonyl group
-al or -aldehyde suffix
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carboxylic acids
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contain carboxyl groups
-COOH
combination of carbonyl group and hydroxyk group
-oic acid suffix
strongly polar
soluable like ketones, aldehydes, and alcohols
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carboxylic acid derivatives
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each contains carbonyl group bonded to oxygen or other elecron-withdrawing element
acids, chlorides, esters, amides
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Amines
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derivative of ammonia
basic
often called alkaloids
name alkyl group bonded to nitrogen + amine
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amides
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acid derivatives that result from combo of an acid with ammonia or an amine
structure of long chain
most stable acid derivatives
strong hydrogen bonds
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nitriles
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compound containing cyano group
(C triple bonded to N)
group is highly polar
somewhat soluable
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Sigma Bonding
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Electron density lies b/w the nuclei
A bond may be formed by s-p, p-p, s-s
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Pi Bond
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forms when parallel orbitals overlap and share electrons
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VSPER
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arrange electron pairs around the central atom so that they are as far away from each other as possible
2: linear, 180
3: triagonal planar, 120
4: tetrahedral, 109.5
5: trigonal bipyramidal, 90, 120, 180
6: octahedral, 90, 180
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sp2
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3 vspr pairs
trigonal planar
120 bond angles
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alkane
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hydrocarbon
single bonds
sp3 carbons
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alkene
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hydrocarbon
double bond
sp2 carbons
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alkyne
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triple bond
sp carbons
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alcohol
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R-OH
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ether
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R-O-R
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aldehyde
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RCHO
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ketone
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RCOR
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ester
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COOR
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carboxylic acid
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RCOOH
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to predict relative boiling points
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look for differences in hydrogen bonding
molecular weight and surface area
dipole moments
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CHEM 301: Ch4 The Study of Chemical Reactions