Organic Test 1 Flashcards
Electronegativity pattern on the Periodic Table
Increases from left to right
How to Calculate Formal Charges and what they are
FC= valence electrons- nonbonding electrons- (1/2)shared electrons
Valence Numbers of first Row elements (B,C,N,O, and halogens)
B=3; C=4; N=5; O=6; Halogen=7
Important criteria when comparing resonance forms (from most important to least)
- As many octets as possible
- As many bonds as possible
- Any negative charges on electronegative atoms
- As little charge separation as possible
pH and acidity
pH< 7 is acidic.
pH=7 is neutral.
pH> 7 is basic.
A Bronsted-Lowry Acid
Any species that can donate a proton
Bronsted- Lowry Base
Any species that can accept a proton
Conjugate Acids and Bases..
If an acid is strong than its conjugate base is ___
Strong acids have weak conjugate bases (and vice versa)
Ka and it’s representation of acid strength
Ka is called the acid-dissociation constant.
The stronger the acid, the larger the Ka value.
Strong acids have Ka’s greater than one.
Most organic acids are weak with Ka values less than 10^-4.
pKa and it’s relation to the strength of an acid
Strong acids generally have a pKa value close to 0.
Weak acids have pKa values greater than 4.
Given acid HA and conjugate base A-
What is the relation?
If an acid HA is strong, it’s conjugate base A- (anionic form) must be more stable. The more stable the conjugate base, the stronger the acid.
Which way is equilibrium favored?
Equilibrium is favored to the right when the strong acid is a reactant and to the left when the strong base is a product.
Electronegativity and stability of a conjugate base
Ex: Rank stability of anions (conjugate base)
NH3 H2O CH4 and HF
Using that, rank the order of acidity of the respective acid.
Conjugate bases increase in stability when they have a more electronegative element.
so, in order of increasing stability:
-CH3 < -NH2 < -OH < -F
Thus, order of increasing acidity:
CH4 < NH3 < H2O < HF
Relationship between size and anion stability.
Compare:
HBr, HCL, HF, and HI
The negative charge of an anion is more stable if it is spread over a larger region of space. Acidity increases down the column as the size of elements increases.
so, in order of increasing stability:
F- < Cl- < Br- < I-
Thus, order of increasing acidity:
HF < HCl < HBR < HI
What does resonance add to anion stability and the strength of acids?
If the negative charge is delocalized (resonance) then the negative charge of an anion is stabilized.
Order of increasing stability:
ethoxide ion < acetate ion < methanesulfonate ion
Order of increasing acidity:
ethanol < acetic acid < methanesulfonic acid
Lewis Acids
Lewis acids accept a pair of electrons and are called electrophiles, “lover of electrons”
Lewis Bases
species with nonbonding electrons that can be donated to form new bonds.
Called neucleophiles.
When orbitals on different atoms interact, they produce ______ that lead to bonding (or antibonding)
molecular orbitals
When orbitals on the same atom interact, they give ________ that define the geometry of the bonds
hybrid atomic orbitals
What are sigma bonds?
All single bonds are sigma bond. Highest electron density in the bonding region between the two protons (for example in H2)
What is a pi bond?
Pi bonds result from overlap between two p orbitals oriented perpendicularly to the line connecting the nuclei.
A combination of a sigma bond and a pi bond is the normal structure of a double bond.
sp hybrid orbitals
Result in a linear bonding arrangement.
Give bond angles of 180 degrees
sp2 hybrid orbitals
Bond angles of 120 degrees, trigonal geometry.
sp3 hybrid orbitals
tetrahedral arrangement oriented 109.5 degrees apart from each other.
Methane is the simplest example
Rotation about single/double bonds
Rotation about single bonds is allowed.
There can be no rotation about a double bond.
Isomers
Isomers are different compounds with the same molecular formula
Constitutional Isomers (structural isomers)
Isomers that differ in their bond sequence.
Stereoisomers
Isomers that differ only in the way their atoms are arranged in space.
Their atoms are bonded in the same order.
cis-trans isomers
the cis isomer is the one with similar groups on the same side of the double bond.
the trans isomer is the one with similar groups on opposite sides of the double bond
Bond dipole moment
A measurement of the polarity of an individual bond.
Defined as (amt of charge at either end of the dipole) multipled by the (distance between the charges)
Molecular dipole moment
The dipole moment of the molecule taken as a whole.
The value of the molecular dipole moment is equal to the vector sum of the individual bond dipole moments
dipole-dipole forces
Attractive intermoleculr forces resulting from the attraction of the positive and negative ends of the dipole moments of polar molecules.
London dispersion force
Aries from temporary dipole moments that are induced in a molecule by other nearby molecules.
A small temporary dipole moment is induced when one molecule approaches another molecule in which the elecetrons are slightly displace from a symmetrical arrangement.
Connection between surface area and boiling point of simple hydrocarbons.
The greater the surface area, the larger the boiling point.
The overarching principle involved is simple: the stronger the noncovalent interactions between molecules, the more energy that is required, in the form of heat, to break them apart. Higher melting and boiling points signify stronger noncovalent intermolecular forces.
Hydrogen Bond
A hydrogen bond can participate in hydrogen bonding if it is bonded to ____, _____, ____.
Not a true bond, but a particularly strong dipole-dipole attraction
A hydrogen bond can participate in hydrogen bonding if it is bonded to Oxygen, Nitrogen, or Flourine.
Organic compounds do not contain H-F bonds, so we consider only O and N.
What is the result of a polar solute with a polar solvent?
Dissolves.
A polar solvent can separate the ions because it solvates them. If water is the solvent, the solvation process is called hydraton.
As the salt dissolves, water molecules surround each ion, with the appropriate end of the water dipole moment next to the ion.
What is the result of a Polar Solute with a Nonpolar Solvent?
Does not dissolve.
The nonpolar molecules of these solvents do not solvate ions very strongly, and they cannot overcome the large lattice energy of the salt crystal.
Attractions of the ions for each other are much greater than their attraction for the solvent.
What is the result of a nonpolar solute in a nonpolar solvent?
Dissolves
The molecules of a nonpolar substance are weakly attracted to each other, and these van der Waals attractions are easily overcome by van der Waals attractions with the solvent.
What is the result of a nonpolar solute in a polar solvent?
Does not dissolve.
For example, gasoline or oil do not dissolve in water because they would have to break up the hydrogen bonds of the water molecules (hydrogen bonding)
Prefix of a 1 carbon chain
methane
Prefix of a 2 carbon chain
ethane
Prefix of a 3 carbon chain
propane
Prefix of a 4 carbon chain
butane
Prefix of a 5 carbon chain
pentane
Prefix of a 6 carbon chain
hexane
Prefix of a 7 carbon chain
heptane
Prefix of a 8 carbon chain
octane
Prefix of a 9 carbon chain
nonane
Prefix of a 10 carbon chain
decane
isobutane
Alkanes
hydrocarbons that contain only single bonds
Alkenes
Hydrocarbons that contain carbon-carbon double bonds
They cannot rotate
Alkynes
Hydrocarbons with carbon-carbon triple bonds as their functional group
Aromatic Hydrocarbons (arenes)
All derivative of benzene.
A six-membered ring with three double bonds.
Alcohols
organic compounds that contain the hydroxyl group (-OH)
General Formula: R-OH
Ethers
Ethers are composed of two alkyl groups bonded to an oxygen atom.
General Form: R-O-R’
Aldehydes and Ketones
Carbonyl group
Both contain the carbonyl group, C=O
A ketone has two alkyl groups bonded to the carbonyl group.
An aldehyde has one alkyl group and a hydrogen atom bonded to the carbonyl group.
Carboxylic Acid
Carboxylic Acids contain the carboxyl group, –COOH
The general formula: R-OOOH
These are combination of the carbonyl and hydroxyl groups
Amines
Amines are alkylated derivatives of ammonia
A Saturated Hydrocarbon
A hydrocarbon with no double or triple bonds
Isobutane
Neopentane
Isopentane
IUPAC Rule 1: The Main Chain
Find the longest continuous chain of carbon atoms, and use the name of this chain as the base name of the compound.
Substituents
The groups attached to the main chain.
What do you do when there are two longest chains of equal length?
Use the chain with the greater number of substituents as the main chain.
IUPAC Rule 2: Numbering the Main Chain
Number the longest chain, beginning with the end of the chain nearest a substituent
IUPAC Rule 3: Naming Alkyl Groups
Name the substituent groups attached to the longest chain as alkyl groups. Give the location of each alkyl group by the number of the main-chain carbon atom to which it is attached.
Butyl Group
isobutyl group
sec-butyl group
tert-butyl group
(or “t-butyl group”)
propyl group
(or “n-propyl group”)
isopropyl group
ethyl group
methyl group
IUPAC Rule 4: Organizing Multiple Groups
When two or more substituents are present, list them in alphabetical order.
When two or more of the same alkyl substituent are present, use the prefixes to avoid having to name the alkyl group twice.
Prefix for
2
3
4
5
6
di= 2
tri= 3
tetra= 4
penta= 5
hexa= 6
Hydrophobic
“water hating”
Alkanes are hydrophobic because they do not dissolve in water.
As the shape of a molecule become more highly branched and compact, the melting point _____
The melting point increases because the compacted shape packs more easily into a solid structure
The melting point curve for even versus odd alkanes.
The melting point curve for alkanes with even numbers of carbon atoms is slightly higher than the curve for alkanes with odd numbers of carbons.
Alkanes with even numbers of carbon atoms pack better into a solid structure, so that higher temperatures are needed to melt them.
Products?
Halogenation
Alkanes can react with Halogens (F,Cl,Br,I) to form alkyl halides.
Structure of Methane
Methane:
Tetrahedral
109.5 degree bond angles
sp3 hybrid carbon.
Conformations
The different arrangements formed by rotations about a single bond.
A specific conformation is called a conformer (or conformational isomer)
Totally Eclipsed Conformation of Butane
Gauche Conformation of Butane
Eclipsed Conformation of Butane
Anti Conformation of Butane
steric strain or steric hindrance
“crowding”
interference between two bulky groups
(ex: Totally eclipsed conformation of Butane)
General Molecular Formula for Cycloalkanes
Formula for determing the unsaturation number
UN= [2(# C)+2-(#H)]/2
If a molecule contains a Halogen, count it as an H
If a molecule contains an Oxygen, ignore it.
If a molecule contains a Nitrogen, subtract the # of nitrogens from the number of hydrogens
What is the meaning of an unsaturation number of 1, 2, 3, etc.
The unsaturation number gives an idea of how many multiple bonds or rings are present in the compound. Each pi bond is 1 point of unsaturation and each ring is 1 point of unsaturated.
Ex:
UN=1 means that the compound has 1 double bond or 1 ring.
UN=2 means that the compound has 2 double bonds, 1 triple bond, a double bond and a ring, or 2 rings.
What are the steps to a systematic isomer hunt?
- Determine the unsaturation number
- Look for structural isomers first.
a) Draw the longest continuous carbon chain (or largest ring). With double/triple bonds, place them in as many different positions as possible.
b) Chop off one carbon and place that carbon in as many different positions on the parent chain as possible. (or construct ring with one less carbon and place one carbon on the ring).
c) Continue until no longer possible. Now have all possible carbon skeletons.
d) if necessary, place halogens place halogen or OH group in as many positions as possible on each of the carbon skeletons. - Look for geometric (cis/trans) isomers
