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79 Cards in this Set

  • Front
  • Back
Lewis Dot Structure
Most basic form of structural formula

3 rules:
1. find total # of valence electrons for all atoms in molecule
2. use 1 pair of electrons to form 1 bond between each atom
3. arrange remaining electrons around atoms to satisfy duet rule for H and octet rule for other atoms
Valence
number of bonds an atom usually forms

C = 4, tetravalent
N = 3, trivalent
O = 2, divalent
H & halogens = 1, monovalent
Formula charge
number of electrons in the isolated atom, minus # of electrons assigned to the atom in lewis structure

sum of formal charges for each atom in molecule or ion represents total charge on molecule or ion
Dash formula
shows bonds between atoms

doesn't show 3D structure of molecule
Condensed formula
does not show bonds

central atoms are followed by atoms that bond to them (even though it is not the bonding order)

ex:
CH3CH2CH2OH
Bond-line formula
line intersections, corners and endings represent a C atoms, unless other atom is drawn in

H atoms attached to C are not usually drawn but assumed to be present
Fischer projection
vertical lines are assumed to be oriented into the page

horizontal lines are assume to be oriented out of page
Newman projection
view straight down axis of 1 of sigma-bonds

both intersecting lines and large circle are assumed to be C atoms
Dash-line-wedge formula
black wedge is assumed to be coming out of page

dashed wedge assumed to be going into page

lines assumed to be in plane of page
ball and stick models
ball = atoms
stick = bonds

3D structure of molecules
Index of Hydrogen Deficiency
# of pairs of H a compound requires in order to become a saturated alkane

saturate alkane contains (2n + 2) # of H, where n = # C

Index of H deficiency = [(2n+2) - x]/2
n: # C atoms
x: # H atoms
count halogens as H, ignore O, count N as 1/2 H

index of H deficiency of saturate alkane = zero
Functional groups
reactive, non-alkane portions of molecules

List #1:
1. alkane
2. alkene
3. alkyne
4. alcohol
5. ether
6. amine
7. aldehyde
8. ketone
9. carboxylic acid
10. ester
11. amide
Alkane
C-C single bond

methane
Alkene
C-C double bond
Alkyne
C-C triple bond
Alcohol
R-OH
Ether
R-O-R
Amine
Primary amine:
R-N-H2

Secondary amine:
R2-N-H

Tertiary amine:
R3-N
Aldehyde
R-C-O-H
Ketone
R-C-O-R
Carboxylic acid
R-C-O-OH
Ester
R-C-O-OR
Amide
R-C-O-NH2
Functional groups
List #2:
1. Alkyl
2. Halogen
3. gem-dihalide
4. vic-dihalide
5. hydroxyl
6. alkoxy
7. hemiacetal
8. hemiketal
9. mesyl group
10. tosyl group
11. carbonyl
12. acetyl
13. acyl
14. anhydride
15. aryl
16. benzyl
17. hydrazine
18. hydrazone
19. vinyl
20. vinylic
21. allyl
22. nitrile
23. epoxide
24. enamine
25. imine
26. tautomers
27. oxime
28. nitro
29. nitroso
Alkyl
1 H substituted from an alkane
Halogen
Halo-

F, Cl, Br or I
Hydroxyl
-OH
alkoxy
-OR
Prefix = C #s
meth = 1
eth = 2
prop = 3
but = 4
pent = 5
hex = 6
hept = 7
oct = 8
non = 9
dec = 10
IUPAC rules for nomenclature
1. longest C chain with most substituents determines base name
2. end C closest to C with substituent is always 1st C. In case of tie, look to next substituent
3. Any substituent is given same # as its C
4. if same substituent is used more than once, use prefixes: di, tri, tetra, etc
5. order substituents alphabetically
Electrostatic force
force between electrons and nuclei that creates all molecular bonds

takes 2 electrons to form a bond

electrons are at lowest energy level when they form a bond because they have minimized their distance from both nuclei

each bonded nuclei can donate a single electron to the bond
Coordinate covalent bond
one nucleus donates both electrons to the bond
Sigma-bond
forms when bonding pair of electrons are localized directly between 2 bonding atoms

lowest energy, most stable form of covalent bond, strong

always 1st type of covalent bond to formed between any 2 atoms

single bond must be a sigma-bond

any double or triple bond, contains 1 sigma-bond
Pi-bonds
additional bonds that form between 2 sigma-bonded atoms

orbital of 1st Pi-bond forms above and below sigma-bonding electrons because sigma-bond leaves no room for other electron orbitals directly between atoms

1 pi-bond = double bond (orbital above and below sigma-bond)
2 pi-bonds = triple bond (orbital on either side of sigma-bond)

weaker and more reactive than sigma-bond, but strengthen and shorten overall bond

C, N, O & S form pi-bonds

pi-bonds prevent rotation
Bond energy
energy necessary to break a bond
Atomic orbitals
s, p, d and f orbitals
Atomic orbitals of lone C atom
C has 4 valence electrons

2 electrons in s subshell
2 electrons in 2 orbitals of p subshell
Atomic orbitals of C with 4 sigma-bonds
4 hybrid orbitals = 4 sigma-bonds

4 electrons in 4 sp hybrid orbitals (equivalent in shape and energy)

hybrid orbital overlap leads to sigma-bond formation in area where orbitals coincide
hybrid orbitals
types:
1. sp
2. sp^2
3. sp^3

add # of lone pairs of electrons to # sigma-bonds and match total # to sum of superscripts in hybrid name (no superscript = 1)

ex: H2O
2 lone pairs + 2 sigma-bonds = 4
4 = 1 + 3 = sp^3
Character
superscripts indicate the character as follows:
sp^2 = 1s + 2p = 33% s + 66% p

hybrid orbitals resemble in shape and energy the s and p orbitals from which it is formed to the same extent that s or p orbitals are used

the more s character a bond has, the more stable, stronger, shorter the bond becomes
hybridization, bond angles and shape
sp = 180 = linear

sp^2 = 120 = trigonal planar

sp^3 = 109.5 = tetrahedral, pyramidal or bent

dsp^3 = 90, 120 = trigonal-bypyramidal, seesaw, T-shaped or linear

d^2sp^3 = 90 = octahedral, square pyramidal or square planar
Resonance structure
2 or more lewis structures representing molecules with delocalized electrons (bonding electrons spread out over 3 or more atoms)

weighed average of these structures represents real molecule (lower energy than lewis structures)
4 rules for resonance structures
1. atoms must not be moved (move electrons, not atoms)
2. # of unpaired electrons must remain constant
3. resonance atoms must lie in same plane
4. only proper lewis structures allowed
2 conditions exist for resonance structures to occur
1. a species must contain an atom either with a p orbital or an unshared pair of electrons
2. that atom must be single bonded to an atom that possesses a double or triple bond (Conjugated unsaturated systems)
Aromatic
rings that display resonance
dipole moment
occurs when center of positive charge (center of mass) on molecule or bond doesn't coincide with center of negative charge

represented by arrow pointing from positive charge to negative charge, arrow is crossed at center of positive charge

measure in units of debye (D)
micron = qd
q: magnitude of charge
d: distance between centers of change
Polar molecule or bond
molecule or bond with dipole moment

results from differences in electronegativity of its atoms

molecules with polar bond may or may not have a dipole moment
Nonpolar molecule or bond
molecule or bond without dipole moment
Induced dipoles
weaker than permanent dipoles

dipole moment is momentarily induced in an otherwise nonpolar molecule or bond by a polar molecule, ion or electric field
Instantaneous dipole moment
electrons in bond move about orbital, and at any given moment may not be evenly distributed between 2 bonding atoms

very short lived and weaker than induced dipoles

can act to induce dipole in neighboring atom
Intermolecular attractions
attractions between separate molecules

occur solely due to dipole moments

must weaker than covalent forces (1% as strong)

attraction between molecules in proportional to their dipole moments
Hydrogen bond
intermolecular bond formed when H is attached to a highly electronegative atom (N, O or F) it creates a large dipole moment leaving H with strong partial positive charge. When H approaches N, O or F on another atom, intermolecular bond is formed
London Dispersion Forces
weakest dipole-dipole force

between 2 instantaneous dipoles

very weak, but are responsible for phase changes of nonpolar molecules
Isomers
unique molecules with same molecular formula

2 molecules are isomers if they have same molecular formula but are different compounds
Conformational isomers (conformers)
not true isomers

different spatial orientations of the same molecule

simplest way to distinguish between conformers is with newman projections
Structural isomer
simplest form of isomer

same molecular formula but different bond-to-bond connectivity

ex:
isobutane and n-butane, both are C4H10, but have different structures
Stereoisomers
2 unique molecules have same molecular formula and same bond-to-bond connectivity
Chirality
handedness of a molecule

chiral molecules differ from their reflections

achiral molecules are exactly the same as their reflections

any C is chiral if it is bonded to 4 different substituents
Absolute configuration
physical description of orientation of atoms about a chiral center (such as a chiral carbon)

2 possible configurations:
1. molecule
2. mirror image of molecule

Determined by R (right) & S (left):
1. atoms attaches to chiral center or #ed from higher (higher atomic weight) to lowest priority (smaller atomic weight)
2. substituents on double and triple bonds are counted 2 or 3 times, respectively
3. lowest priority group faces away
4. circle is drawn from lowest to higher priority
5. clockwise (R) and counter-clockwise (S)
6. mirror image always has opposite absolute configuration
Relative configuration
not related to absolute configuration

2 molecules have the same relative configuration about a C if they differ by only 1 substituent and other substituents are oriented identically about C
Observed rotation
direction and degree to which a compound rotates plane-polarized light
Polarimeter
screens out photons with all but one orientation of electric field

resulting light consists of photons with their electric fields oriented in same direction
Plane-polarized light
white light that has passed through a polarimeter and now has photons all oriented in same direction
Optically inactive
may be compounds with no chiral centers or contain equal amounts of both stereoisomers

compound does not rotate light

no single molecular orientation is favored, so there is no rotation of plane of electric field.
Racemic mixture
optically inactive compound

contains equal amounts of both stereoisomer therefore no rotation of light is observed
Optically active
compound that rotates light, orientation of electric field is rotated

racemic mixture is separated, resulting in compound containing molecules with no mirror images

if rotates plane-polarized light clockwise = + or d (right)

if rotates plane-polarized light counter-clockwise = - or l (left)
Observed rotation
direction and # of degrees that electric field in plane-polarized light rotates when it passes through a compound
Specific rotation
standardized form of observed rotation

calculated from observed rotation and experimental parameters
Stereoisomers
2 molecules with same molecular formula and same bond-to-bond connectivity that are not same compound

unless geometric isomers, stereoisomers much each contain at least 1 chiral center in same location

2 types:
1. enantiomers
2. diastereomers
Enantiomers
same molecular formula

same bond-to-bond connectivity

mirror images of each other

not same molecule

opposite absolute configurations at each chiral C

rotate plane-polarized light in opposite directions to an equal degree

same physical and chemical properties except:
1. reactions with other chiral compounds
2. reactions with polarized light

make racemic mixture, when mixed together in equal concentrations
Resolution
separation of enantiomers
Diastereomers
same molecular formula

same bond-to-bond connectivity

not mirror images to each other

not same compound
Geometric isomer
type of diastereomer

exist due to hindered rotation about a bond (ring structure, double or triple bond)

different physical properties

1. 2 substituents on each C are prioritized using atomic weight
2. higher priority substituent for each C on opposite sides = E
3. higher priority substituent for each C same side = Z
Cis-isomers
diastereomers

geometric isomers

molecules with same side substituents

have dipole moment

stronger intermolecular forces leading to higher boiling points (due to dipole moment)

do not form crystals as readily leading to lower melting points (due to lower symmetry)

steric hindrance (substituents crowd each other) produce higher energy levels resulting in higher heats of combustion
Trans-isomers
diastereomers

geometric isomers

molecules with opposite-side
substituents

do not have dipole moment
Maximum # of optically active isomers
2^n
n: # of chiral centers
Meso compounds
2 chiral centers in a single molecule may offset each other creating an optically inactive molecule

plane of symmetry through their centers which divides them into 2 halves that are mirror images to each other

are achiral and therefore optically inactive
Epimers
Diastereomers that differ at only 1 chiral C
Anomers
chiral C is called an anomeric C

distinguished by orientation of substituents

when ring closure occurs at epimeric C, 2 possible diastereomers may be formed

ex:
1. alpha-glucose (OH oriented opposite direction of CH3)
2. beta-glucose (OH oriented same direction of CH3)