chm136 test 1 Flashcards
rules for comparing resonance forms
- full octet
- less formal charges
- neg charge on more EN atoms, pos charges on more electropositive atoms
- same charges far away, opp. charges close
delocalized pi bond is…
when 2 electrons are shared among 2+ atoms
what is necessary for resonance?
pi bonds or lone pairs
resonance atoms are always ___ hybridized
sp2
valence electrons are…
electrons in an orbital in an unfilled shell
covalent bonding involves
1 electron from e/ bonding atom of opp. spin
formal charge formula
group # - # bonds - # non-bonded electron
sp3 hybrids = … (composition)
1x 2s, 3x 2p orbitals (25% s character and 75% p character), sppp
what does sp2 have that’s unique (specific orbital)
an unhybridized 2pz orbital that’s perpendicular to the sp2 plane
how are sp2 hybridized orbitals oriented
3 sp2 orbitals oriented on a plane, unhybridized 2pz orbital perpendicular to that`
sp hybrid structure
1x 2s, 1x 2p with 2 unhybridized 2p orbitals (all perpendicular)
constitutional isomers
molecules w/ the same molecular formula but diff bonding
nitrile (structure)
C triple bond N
organohalide
C-X, X = F, Cl, Br, I
inductive effect
difference of electron density in a bond due to differences in EN
electrons moving through sigma bonds is called
induction
electrons moving through pi bonds is called
resonance
types of IMF
dip-dip, H bonding, LDF, electrostatic interactions
electrostatic interactions
opp formal charges attracting
polar protic solvents
H-bond donors, v polar
polar aprotic solvents
mostly H-bond acceptors, strong polar dipoles w/o H bonds
non polar solvents
no significant polarity/net dipole
degree of unsaturation formula
(2C + 2 - H + V - VII)/2
how are ions separated in mass spectrometry
separated based on mass to charge ratio - all ions have the same charge
M+ peak?
indicates mass of molecule - it’s the highest heaviest peak
M+1 peak?
detects heavier isotopes
what does spectroscopy measure
interaction b/w a molecule and EM radiation
what does infrared spectroscopy measure
bond vibration - stretching, bending
(IR spectroscopy) relationship between frequency, strength and mass
inc freq = inc strength = dec mass
what types of bonds can absorb IR
polar bonds only (although bonds with slight dipoles still show up on IR)
what does intensity of signals on IR tell you
how polar the bonds are
what do broad peaks indicate
H bonding
which C-C bond is diagnostic
triple bond
what is important to note when looking at IR
symmetry around bonds of the molecule (particularly when looking at C-C and C-H bonds)
main sections of IR spectrum
hydrogen region, trip bond region, double bond region, fingerprint region
what does NMR map
protons/H with unique electronic environments
how do neighbouring atoms influence a nucleus’s magnetic environment
electron rich nuclei are more shielded and show up at lower ppm, EN atoms deshield H (H close to EN atoms are less e- rich), pi bonds have a deshielding effect (signals will appear more upstream/higher ppm when pi bond exists)
what does it mean to be on the left side of the NMR
close to EN atoms and whatnot
integration spectrum
ratio of # of H at e/ signal
torsional strain
repulsion b/w neighbouring substituents (staggered vs eclipse conformation)
steric strain
repulsion from when atoms that are not bonded to e/o are forced to be close to one another - ie large groups too close to e/o (anti vs gauche)
angle strain
arise from bond angles that don’t permit max orbital overlap b/w atoms of a molecule (ideal is 109.5)
1-3 diaxial strain is a type of …
steric strain
stereoisomers (types, _/ vs _)
cis vs trans
steric strain vs torsional strain
torsional strain is from overlapping substituents, steric is from BIG overlapping substituents
