Unit 2: Structural effects

Intramolecular forces

are forces that holds atoms together within a molecule

intermolecular forces

are forces that exist between molecules.

Non-polar covalent
Polar Covalent
Ionic Bond
Metallic Bond

what is the relative strength of each intramolecular force from lowest to highest

London Dispersion forces
Dipole-Dipole Attraction
Hydrogen bonding

Relative strength and polarity of each Intermolecular force for lowest to highest

Intermolecular force

force of a covalent bond

Hydrogen bonding

is the strongest intermolecular bonding

Sulfur, Oxygen or nitrogen

if hydrogen is bonded by one of these then it is automatically hydrogen bonding

Dipole-dipole attraction

exists whenever there is electronegative atom (O, N)

bond with S,O,N,X and should be assymetrical

what are the requirements for a dipole-dipole attraction

London dispersion force

exists in carbon-carbon/carbon-hydrogen bonding

C-C/C-H

requirement for london dispersion force

Solubility

follows the principle of "like dissolves like"; chemical with similar IMF are bound to dissolve with each other.

like dissolves like

what principle does solubility follows

polar IMF

water exhibits what IMF

C-C/C-H

what are examples of non polar imf

directly proportional

relationship between polarity of IMF and solubility

Branching

it allows space for H2O = ↑ solubility

directly proportional

relationship of branching and solubility

directly proportional

relationship of IMF to Boiling point and melting point

directly proportional

relationship of length of carbon chain to boiling point and melting point

Inversely proportional

Relationship of Branching carbon linkage to boiling point and melting point

Structural effects

These are effects of the structure of an organic compound to its stability and reactivity.

pi-bond delocalization
CH hyperconjugation
Lone-pair delocalization
Inductive effect
Steric effect

what are the different structural effects

Pi-bond delocalization

The electrons being shared by the sideway overlap of unhybridized p-orbitals are able to delocalize into nearby unhybridized p-orbital resulting into rearrangement of the bonds in the structure.

Pi-bond delocalization

structural effect that are common in sp2 and sp-hybridized carbons.

series of 3 consecutive sp2

what is the requirement for pi-bond delocalization

sp2 and sp-hybridized

pi-bond delocalization is common in where

pi-bond delocalization

results into the formation of canonical structures or resonance structures.

Directly proportional

relationship of canonical structures or resonance structures to stability

canonical or resonance structures

pi-bond delocalization will form what

CH hyperconjugation

also known as sigma electron release

sigma electron release

CH hyperconjugation is also known as what

CH Hyperconjugation

where the electron shared in the head-on overlap between an sp3 hybridized carbon and a hydrogen atom is delocalized towards a nearby sp2 or sp hybridized carbon.

CH hyperconjugation

The delocalization results into one (1) hydrogen/proton being cleave from an sp3 carbon and being bonded to another δ- carbon.

consecutive 2 sp2 and 1 sp3

requirement for CH Hyperconjugation

lone-pair electrons

are two (2) valence electrons which do not participate in bond formation (unshared). They occupy an orbital and can be delocalized into nearby unhybridized p orbitals

N, O, S

common atoms that will undergo lone-pair delocalization

inductive effect

is a phenomenon wherein the charge of a chemical bond affects orientation of adjacent bonds in a molecule, resulting into a permanent polarization.

if the atom is qualified for pi-bond delocalization, CH hyperconjugation, and Lone-pair delocalization

requirement for inductive effect

Electron releasing/repelling inductive effect (example: alkyl groups)
Electron withdrawing/attracting inductive effect (example: halides)

Molecules are grouped into two based on their inductive effect which are what

alkyl groups

what group of atoms have electron releasing/repelling inductive effect

Halides

what group of atoms have electron withdrawing/attracting inductive effect

Electron releasing/repelling effect

Atoms of molecules which attracts electrons less strongly relative to hydrogen, thus resulting to a positive inductive effect (+I effect).

(CH3)3C < (CH3)2CH < CH3CH2CH2 < CH3CH2 < CH3 < H

examples of electron-releasing groups

Electron-withdrawing/attracting groups

Atoms of molecules which attracts electrons more strongly relative to hydrogen, thus resulting to a negative inductive effect (-I effect).

N+(CH3)3 > NO2 > CN > F > COOH > Cl > Br > I > CF3 > OH > OCH3 > C6H5 > H

examples of electron attracting groups

Steric effect

is the resulting structural effect due to the presence of bulky or huge substituents attached to the organic molecule

bulky or huge substituents

Steric effect is the resulting structural effect due to what attached to the organic molecule

instability of molecule

The presence of steric effect may result to what and may also affect reactivity of the organic molecule.

Brønsted-Lowry Acid

is a substance that donates a proton (H+).

Brønsted-Lowry Base

is a substance that accepts a proton (H+).

Acidity constant (Ka)

Based on the Brønsted-Lowry definition of acids and bases, the strength of acids is expressed using what

pKa

is the negative common logarithm of Ka

Lewis acid

is a substance that accepts an electron pair.

Lewis base

is a substance that donates an electron pair. The electron pair is then shared covalently between the acid and base.