Organic Test 1
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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