exam 1 material

overarching principle of orgo

overarching principle of orgo

structure implies function/properties

what scientist and procedure type contributed to early orgo knowlege

justun von liebig and his elemental analysis - where he burned organic molecules and studied their products

what did liebig’s experiments show

a formula appearing in chemical patters - molecules who’s formula followed a specific pattern acted similarly

basic alkane formula

Cn H(2n+2)

basic alkene formula

Cn H2n

basic alkyne formula

Cn H(2n-2)

what important hypothesis was made about carbon

it was tetravalent - formed as a result of the patterns in the molecular formulas

who contributed to the carbon hypothesis

buterov, kekule, and cooper

paraffin

another name for linear alkanes, specifically those with a high molecular weight where n = 22 - 27 ; not very reactive

difference between alkane, alkene, and alkyne

ane = all single bonds, fully saturated
ene = at least 1 double bond, unsaturated
yne = at least 1 triple bond, unsaturated

if there’s a ring in a molecular structure, what happens to the name

the prefix cyclo- goes in front of the usual name

are saturated or unsaturated molecules more reactive

unsaturated - bc they have 2x and 3x bonds that’re weaker than the 1x bonds in saturated hydrocarbons (bc of pi bonds) so when a reaction happens, they break down more easily

degrees of unsaturation

1 - a ring or 2x bond
2 - 2 2x bonds, a 3x bond, a ring and 2x bond, 2 rings, etc.
3 - 3 rings, 3 2x bond, etc.

calculation for degrees of unsaturation

1 + ½ the sum of all n(v-2) OR number of rings + multiple bonds
where n is the number of atoms of one species of atom and v is that species’ valence

example calculation of degrees of unsaturation for cycloproene

cyclopropene has a ring and a 2x bond so it should be 2
OR
1+1/2 [3(4-2) + 4(1-2)] = 2
bc there’s 3C and C has a valence of 4, 4H and H has a valence of 1

valence

the number of bonds an atom can have
8 - #ve of the atom = # bonds the atom wants

isomers

molecules with the same molecular formula but different structures

constitutional isomers / structural isomers

same molecular formula, but have different connectivity

connectivity

the way atoms are connetced

stereoisomers

isomers that differ in spatial arrangement of atoms, rather than order of atomic connectivity

example of isomers - C2H2Cl2 (identify and draw)

3 isomers, 1 is a constitutional one with both Cl atoms on one C atom (1,1-dichloroethene) and 2 stereoisomers (1,2-dichloroethene) with the Cl atoms on different C atoms but in different positions (trans vs cis)

cis vs trans isomers

cis - same connectivity of atoms, side groups placed on the same side of a double bond, almost always polar
trans - side groups placed on opposite sides of a double bond

what was van’t Hoff’s contribution to orgo

first to make molecular models to explain isomer bonding - used folded tetrahedrals and distributed them

order of intuitive problems given formula

formula → calculate saturated/unsat → degrees of unsaturation → list potential “special” structure → draw

0 point energy

lowest possible energy that a quantum mechanical system may have at absolute 0 temp - however, even then bonds are moving, stretching, and vibrating

what’s the quantitative problem with von’t hoff’s tetrahedral model

it doesn’t accurately predict the bond angles, geometry, or bond length of molecules with a C-C 2x or 3x bond
it predicts that c-c 2x bond length is 0.885 and the 3x bond is 0.551, but in reality, it’s closer to 1.33 and 1.203 respectively

wave-particle duality

e- have a dualistic nature where sometimes they act like waves while other times they act like particles, depends on the experiment being used

what do e- in atoms act like

standing waves

standing wave

formed by the superposition of 2 travelling waves of the same frequency going in opposite directions

wave symmetry

symmetry of the wave must match the symmetry of the atom, which is spherically symmetrical, so standing waves must also be spherically symmetrical

bond dissociation energy

the energy required to break a chemical bond

where do bonds come from

constructive interference (from mo diagrams) that is a quantum mechanical effect

consequences of quantum mechanics

the pauli exclusion principle, 2e- = 1 bond, octet rule, valence rule

condensed structure

molecules drawn with groups like CH3 and OH instead of having them separated

zig zag / bond line structures

the minimalist lines that only show carbon chains and special attachments

kekule structures

molecules held together with bonds represented by lines, everything separated

what to remember about drawing isomers

molecs defined by longest carbon chain and atoms can rotate around single bonds, so a t-shape is the same as a straight line with a little bit sticking up from the middle

what to remember about adding something like a Cl or Br to a molec and drawing isomers

draw the molec first and then id all the places were the “special” atom could go

how do you get hybrid orbitals

add and subtract atomic orbitals - done by taking a cross section of them and imagining it was on a graph with the nucleus at 0,0 ; then comparing the two orbitals quadrant by quadrant

what does sp orbitals look like

2 “normal” p orbitals (probably y or z) and a px orbital that looks weird - 2x sided with each side having a small ‘nub’ circle and a larger one connected to it on the back so the two ‘nubs’ connect to each other around the nucleus with the larger spheres sticking out back

describe sp orbital formation

2s orbital is basically a big sphere with a smaller circle inside of it (each one is opp charged) and the 2px orbital looks like two circles separated by a planar node (y axis) that’re opp charged
consider + and -:
+ : right of the y axis in both is pos charged so that portion grows in size (pos + pos) while the left is a neg (from 2p) and pos (from 2s) so it shrinks (pos + neg) - the small neg bit in the 2s makes the orbital look more like a 2p one with the smaller neg circle crossing 0,0 and the larger pos circle separated from it by a conical node to the right of the y axis
- : basically the same as the + one but opposite so the larger pos circle is on the left side of the y axis bc the 2s pos - 2p neg = larger pos and the 2s pos - 2p pos = smaller neg

if there’s 2 orbitals contributing to a hybrid orbital, how man hybridized orbitals are ther

2 - in this case, 2s and 2px = sp

hybrid orbitals are quantum mechanical?

nope, mathematical

are hybridized orbitals real

not really, they’re a construct that was invented to adapt atomic orbitals to experimental molecular geometry and are used bc we can’t actually solve schrodinger’s equation for any atoms

px, py, and pz are sphereically symmetrical when you put them together around a nucleus so

the 4 sp3 hybridized orbitals must also be spherically symmetrical and has a tetrahedral geometry

resonance hybrids

different resonance structures that only change where electrons move, not order or how atoms are connected

why does hybridization occur

minimizes e- repulsion and the oversized front of hybrid orbitals overlap better and it causes an energy reduction bc of the better bonding

what do newman projections show

a c-c bond viewed from the front

staggered vs eclipsed newman projections

staggered is more stable bc it minimizes repulsion btwn atoms

anti-conformation

when there are “special” atoms are 180* apart from each other on the newman projections
more stable bc the “special” groups are the furthest away from each other that they can possibly be

gauche conformation

less stable than the anticonformation but more stable than other things
“special” groups in newman structures are 60* and 300* away from each other

anticlincal conformation

an eclipsed conformation of a newman structure that’s 3rd most stable - eclipse = not stable but at least the CH3s aren’t eclipsing each other
“special” groups are 120 and 240* apart from each other

total eclipse conformation

this is unstable and bad because the C atoms are eclipsing each other and have the most repulsion - most unstable bc the C are 0* apart

on a potential energy diagram, what do newman projections look like

the peaks and dips of the graph - the lowest dip has the lowest potential energy and is the most stable and the peaks are the more unstable projections

gauche interactions

where two c atoms or “special” groups are next to each other on the circle and repel
methyl-methyl interactions are where two methyl groups are next to each other, methyl-ethyl are when a methyl and ethyl group have a gauche interaction, etc.
the more gauche interactions in a conformation = less stable
more methyl-ethyl interactions = less stable

compare the energy strains in eclipsed newman structures

if all energy strain values not given, compare the structures with at least 2 identical overlaps and add up the known energy strains to compare their totals

example of where the hybridization model fails

determining the hybridization of the o in dimethyl ether (O(CH3)2) bc it could be pyramidal bc of the lone pairs but the O could also be planar bc there’s no 3rd atom to solidify if it’s planar or not (either distorted tetrahedral or heavily distorted triagonal) - goes back and forth btwn the 2 geometries
ALSO
with methoxide (-OCH3) because the O is only connected to the C so there’s no geo information so it could be sp3 or sp2 or sp with the lone pairs in p orbitals

orbital model

rationalizes the valence rules and the violations of those rules
ex. like how O wants 2 bonds bc it has 2 e- that aren’t paired in orbitals but atoms like N can have 3-4 bondsi

isoelectronic

different molecules with the same number of valence electrons and the same atom connectivity
ex. NH3, NH4-, CH4, etc.

sp2

has to be planar - anything that isn’t planar isn’t sp2

lewis acid

accepts e- pairs
aka electrophiles

lewis base

donates e- pairs
aka nucleophiles

what does a high pka indicate

high proton affinity, stronger bonds, weaker acids, doesn’t give up protons easily

what does a low pka indicate

low affinity for protons, binds protons weakly, gives up protons easily, strong acids

if you break a weaker bond to make a strong one, what does that indicate about Keq

it’s greater than 1

another trick to find Keq

10^delta pka
(final - initial) → if delta pka is -, then Keq is less than 1 and reactants are favored at equilib

what does it indicate when there’s a curved arrow pointing from a bond to a highly electroneg atom

the bond breaks and the 2 e- go to the highly electroneg atom

what does it indicate if there’s a curved arrow starting at an atom and going to another atom

a covalent bond forms between the two - the arrow should be starting at more electroneg and going to lower electroneg atom

what are hybrid and unhybridized orbitals used for

hybrid - forming sigma bonds, unhybridized - forming pi bonds

what is formal definition of pka

ph at which 50% of the acid is dissociated

where does equilib generally lie

on the side with the weaker acid (more + / less - pka value)

what does the electronegativity that the atom connected to the acidic proton say about the bond strong and proton acidity

more electroneg the atom connected to the atom w/ the acidic proton is, the more polar/strong the bond is = more acidic proton

what does the s orbital character have to do with electroneg

the greater the s character of the orbital on atom A is bonded with the acidic proton, the more electroneg A is bc it attarcts e- in the orbital more strongly
ex. acidity of C-H bond inc as hybridization of C goes from sp3 → sp2 → sp

inductive effect

proximity of A to another electroneg atom stabilizes A- and inc the acidity of the proton bonded to A bc of the transmission of e- attracting power

inc A size does what more acidity

inc atom size = less electroneg = lower polarity = weaker bond = higher acidity
acidity of HA inc right and down of PT

what happens in a lewis acid/base rxn

an e- pair moves from the base to the acid

what is generally true about alkanes

usually nonpolar and unreactive

where does polarity come from

difference in electroneg

alcohols

come frmo a hydroxy group : R-OH
end in -ol

ethers

R-O-R’

haloalkanes

halogen like Cl or Br attached to carbon chain
add bromo or chloro or whatever to the name

aldehydes vs ketones

aldehydes - CH=O - the carbonyl group is at the end
ketone - RC(=O)R’ - carbonyl group is in the middle

carboxylic acids

C(=O)-OH

amines

NH group or R-NR’-R’’

amides

C-Cr’-r’’

what happens when you replace O with S in a lot of organic molecules

you change something in the name to be thiol - usually its a prefic

general rule about melting points and boiling points in alkanes

number of carbons in, so does the melting, boiling, and density

alkyl group

formal name for stuff like methyl, ethyl, etc that are substituents attached to carbon chains - created by removed an H from the methane and replacing it with a C

primary C vs secondary C

primary - C that is only attached to one other C
secondary - C attached to two other Cs

general bond angle btwn c-c in alkanes

109*

differences btwn branched and straight alkanes

branched have smaller surface area so they have smaller LDS and can’t pack as solidly into a crystal state so they have lower melting and boiling points

weird nomenclature things that do with chains

if a molec has 2+ chains of equal length, the chain with the most substituents is the “base chain” and determines that number-ane name
if there’s a longer c chain that’s complex and coming off the main one, name it like: #C chain is attached(name of chain like it’s a separate molec)

dihedral angles

angle between atoms in the newman projections, usually for “special” atoms or groups like C or CH3 - need 4 points to define
staggered - 60, 180, 120, 240, 300
eclipsed - 0, 360

where is energy the lowest when mapping a newman structure

lowest at the staggered conformations where the “special” atom/groups are the furthest apart and peaks at 0 and 360 degrees, where the “special” atoms and groups eclipse each other

general rule of thumb about Ch/Ch eclipsing

it lasts about 10^-11 seconds and destabilizes about 1.0kcal/mole of energy

why do eclipse conformations happen at all if they’re so unfavorable

molecs bump into each other and transfer electrons so the molec has thermal energy to isomerize

what kind of interactions are in a staggered propane newman molec? what about in eclipsed?

staggered - none
ecl - 2 Ch/Ch ones (bc the 2C atoms in propane have H attached to each of them that are interacting) and CH/CC interaction (bc one C atom has the CH3 that eclipses an H of the other C atom
remember that newman projection represents the bond btwn 2 C atoms

what kinds of interactions in newman structures are hte most destabilizing? what about least?

least - CH/CH bc the 2 H are just repelling each other and they’re small
most - more C atoms = more destabilizing

how can we find which interactions destabilize what amount of energy

generally, CH/CH destabilizes 0.9 - 1.0 kcal/mole and we assume they act additively so you can ± to figure it out given the total
ex. continuation of propane: we have 2 CH/CH interactions and 1 CH/CC and are given that the total rotation barrier = 3.4kcal/mol
so 3.4 - 2(1.0) = 1.4 kcal/mole is how much is destabilized by the CH/CC interaction

gauche interaction

relationship between two atoms or groups whose dihedral angle is between 0 and 120 - the “Special” atoms interact in the staggered conformation
ex. in butane, we have 2 CH3 groups (1 on each C atom) and the gauche conformation would have 1 CH3 at 0 degrees and the other being at 60 degrees away from it in either direction
2nd most stable interaction so it has the 2nd lowest energy