5 STRUCTURE & SHAPE OF ORGANIC MOLECULES Flashcards
what exerts greater repulsive force? lone or bonding pairs?
lone pairs exert greater repulsive force
what are functional groups?
atom/group of atoms that have a specific structure/sequence. these groups convey certain physical/chemical properties for a molecule
what are hydrocarbons?
compounds containing only carbon and hydrogen
what are alkanes?
contains a single c bond. c-c
what are alkenes?
contains a double c bond. c=c
what are alkynes?
contains a triple c bond.
what are aromatic compounds?
ring with double/single c bonds.
what are alkyl/aryl halides?
halogen connected to alkane/aromatic compound
what are alcohol?
hydroxl group (OH) connected to carbon, etc. single bond w carbon
what ether?
oxygen and element connected to carbon, etc. single bond w carbon
what are amines?
nitrogen connected to carbon,etc. single bond w carbon
what are aldehydes?
oxygen double bonded to carbon. hydrogen bonded to same carbon
what are ketones?
oxygen double bonded to carbon.
what are carboxylic acids?
oxygen double bonded to carbon. hydroxyl connected to the same carbon.
what are esters?
oxygen double bonded to carbon. another oxygen single bonded to same carbon.
what are amides?
oxygen double bonded to carbon. nitrogen single bonded to same carbon
why are specific wavelengths of light absorbed by molecules?
because energy levels are quantized
what does IR absorption correspond to?
bond vibrations (specific molecular motions). IR energy is absorbed when frequency of light matches the “normal” frequency of vibrations for that bond
molecular bonds can be thought of as…?
balls and springs that vibrate as a harmonic oscillator
what is k in regard to the harmonic oscillator?
force constant that is proportional to strength (“stiffness” of the bond)
what is μ in regard to the harmonic oscillator.
is the reduced mass. a value that compensates for the two different masses in the bond (harmonic oscillator)
in the harmonic oscillator, what does a large k indicate?
a tighter spring aka STRONGER BOND! also larger k=higher energy vibrations
how does mass affect bonds?
lighter atoms = higher energy vibrations = stronger bonds
what is the formula for alkanes?
Cn H(2+2)
what can be said for larger molecules?
large = more surface area = more dispersion forces = higher boiling point
what is constitutional isomerism?
same molecular formula but different connectivity/bonding sequence
what are conformations?
quick? spatial arrangements resulting from rotations around single bonds. THEY ARE NOT ISOMERS!!!
what has higher energy? eclipsed or staggered?
eclipsed conformations have higher energy due to repulsion
what is steric repulsion?
if same atoms get too close to each other, more repulsion = higher energy = more unstable
what is the formula for cycloalkanes?
CnH2n
what can be said bout rotation with cycloalkanes?
rotation around c-c single bond is hindered
what are cycloalkanes?
ring of carbon atoms connected by single carbon bonds
what can be said bout rotation with
there is some c-c rotation, but restricted
what are the types of cyclohexane conformers?
boat and chair
how common are boat conformations? chair conformations?
the occurrence of boat conformers is less than 0.1%. the rest is chair conformers
all the substituents in a chair conformer are…?
staggered
what are axial substituents? for what type of conformer?
six substituents directed up and down. this is for the chair conformer of cyclohexanes
what are equatorial substituents? for what conformer?
substituents are pointing laterally away from the ring’s center point. for the chair conformer of cyclohexanes
what is flexing in regard to conformers? (flipflop)
axial substituents change to equatorial positions (vice versa)
what is important to note about steric hindrance and conformers?
molecules tend to adopt most stable conformer - the conformation with least steric hindrance
when is cis-trans stereoisomerism possible in cyclohexanes?
when two or more non-hydrogen substituents are on different carbon rings
why do cis-trans isomers not convert at rotations?
because they are isomers and not conformers
what does unsaturated mean?
the molecule doesnt contain the max # of possible hydrogen atoms. compounds with fewer than 2n+2H atoms are said to be unsaturated
what is the formula for alkenes?
CnH2n
what is the formula for alkynes?
CnH2n-2
when can a double bond only have cis geometry? why?
in rings with 7 members or less, a double bond can only have cis geometry because the trans arrangement would be too strained
what is the formula for max number of cis/trans isomers?
n being number of c=c bonds. 2^n. 2 to the power of n
what is chirality?
type of stereoisomerism.
what can be said about chiral objects?
chiral objects have no plane of symmetry and their mirror images are non superimposable.
what can be said about achiral objects?
achiral (nonchiral) objects have a plane of symmetry and their mirror images are superimposable
what are enantiomers?
same formula and bonding sequence. no plane of symmetry and non superimposable images
two enantiomers have the same physical/chemical properties, except…
act/rotate on plane-polarized light differently.
react with other chiral molecules differently
what are stereocenters?
aka chiral centers. atom in middle of diff substituents (no plane of symmetry)
what are fischer projections?
representation of 3D structure of molecules with chiral carbons
what about chirality in biomolecules? give example and state effects of its R form and S form. what can be learned from this example?
thalidomide.
r form: anti nausea effect for pregnant women.
s form: teratogen - causes birth defects.
chemicals can pass through placental barriers
what rotates plane polarized light? (ppl)
optically active molecules are chiral and rotate ppl. achiral molecules can not.
enantiomers rotate ppl in opposite directions.
how does +/- rotate molecules? is this related to R/S
+ to the right, - to the left. nope they are both independant
