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79 Cards in this Set
- Front
- Back
Lewis Dot Structure
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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 |
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Valence
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number of bonds an atom usually forms
C = 4, tetravalent N = 3, trivalent O = 2, divalent H & halogens = 1, monovalent |
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Formula charge
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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 |
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Dash formula
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shows bonds between atoms
doesn't show 3D structure of molecule |
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Condensed formula
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does not show bonds
central atoms are followed by atoms that bond to them (even though it is not the bonding order) ex: CH3CH2CH2OH |
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Bond-line formula
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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 |
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Fischer projection
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vertical lines are assumed to be oriented into the page
horizontal lines are assume to be oriented out of page |
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Newman projection
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view straight down axis of 1 of sigma-bonds
both intersecting lines and large circle are assumed to be C atoms |
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Dash-line-wedge formula
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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 |
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ball and stick models
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ball = atoms
stick = bonds 3D structure of molecules |
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Index of Hydrogen Deficiency
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# 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 |
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Functional groups
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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 |
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Alkane
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C-C single bond
methane |
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Alkene
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C-C double bond
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Alkyne
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C-C triple bond
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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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Amine
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Primary amine:
R-N-H2 Secondary amine: R2-N-H Tertiary amine: R3-N |
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Aldehyde
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R-C-O-H
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Ketone
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R-C-O-R
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Carboxylic acid
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R-C-O-OH
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Ester
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R-C-O-OR
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Amide
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R-C-O-NH2
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Functional groups
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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 |
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Alkyl
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1 H substituted from an alkane
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Halogen
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Halo-
F, Cl, Br or I |
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Hydroxyl
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-OH
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alkoxy
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-OR
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Prefix = C #s
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meth = 1
eth = 2 prop = 3 but = 4 pent = 5 hex = 6 hept = 7 oct = 8 non = 9 dec = 10 |
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IUPAC rules for nomenclature
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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 |
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Electrostatic force
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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 |
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Coordinate covalent bond
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one nucleus donates both electrons to the bond
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Sigma-bond
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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 |
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Pi-bonds
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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 |
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Bond energy
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energy necessary to break a bond
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Atomic orbitals
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s, p, d and f orbitals
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Atomic orbitals of lone C atom
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C has 4 valence electrons
2 electrons in s subshell 2 electrons in 2 orbitals of p subshell |
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Atomic orbitals of C with 4 sigma-bonds
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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 |
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hybrid orbitals
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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 |
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Character
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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 |
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hybridization, bond angles and shape
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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 |
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Resonance structure
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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) |
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4 rules for resonance structures
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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 |
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2 conditions exist for resonance structures to occur
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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) |
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Aromatic
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rings that display resonance
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dipole moment
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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 |
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Polar molecule or bond
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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 |
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Nonpolar molecule or bond
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molecule or bond without dipole moment
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Induced dipoles
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weaker than permanent dipoles
dipole moment is momentarily induced in an otherwise nonpolar molecule or bond by a polar molecule, ion or electric field |
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Instantaneous dipole moment
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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 |
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Intermolecular attractions
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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 |
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Hydrogen bond
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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
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London Dispersion Forces
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weakest dipole-dipole force
between 2 instantaneous dipoles very weak, but are responsible for phase changes of nonpolar molecules |
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Isomers
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unique molecules with same molecular formula
2 molecules are isomers if they have same molecular formula but are different compounds |
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Conformational isomers (conformers)
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not true isomers
different spatial orientations of the same molecule simplest way to distinguish between conformers is with newman projections |
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Structural isomer
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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 |
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Stereoisomers
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2 unique molecules have same molecular formula and same bond-to-bond connectivity
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Chirality
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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 |
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Absolute configuration
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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 |
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Relative configuration
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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 |
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Observed rotation
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direction and degree to which a compound rotates plane-polarized light
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Polarimeter
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screens out photons with all but one orientation of electric field
resulting light consists of photons with their electric fields oriented in same direction |
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Plane-polarized light
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white light that has passed through a polarimeter and now has photons all oriented in same direction
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Optically inactive
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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. |
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Racemic mixture
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optically inactive compound
contains equal amounts of both stereoisomer therefore no rotation of light is observed |
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Optically active
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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) |
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Observed rotation
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direction and # of degrees that electric field in plane-polarized light rotates when it passes through a compound
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Specific rotation
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standardized form of observed rotation
calculated from observed rotation and experimental parameters |
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Stereoisomers
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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 |
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Enantiomers
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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 |
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Resolution
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separation of enantiomers
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Diastereomers
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same molecular formula
same bond-to-bond connectivity not mirror images to each other not same compound |
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Geometric isomer
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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 |
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Cis-isomers
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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 |
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Trans-isomers
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diastereomers
geometric isomers molecules with opposite-side substituents do not have dipole moment |
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Maximum # of optically active isomers
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2^n
n: # of chiral centers |
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Meso compounds
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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 |
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Epimers
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Diastereomers that differ at only 1 chiral C
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Anomers
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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) |