Fundamentals of Organic Chemistry

Fundamentals of Organic Chemistry

Inductive Effect

Steric Hindrance

Hydrogen Bonding

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Nature of electron cloud

What is an electron cloud?

The term electron cloud describes the area around an atomic nucleus where electrons will probably be.

Electron Density

Atomic Bonds become more polarized when the difference between electronegativity of the atoms is large.

Inductive Effect

Polarization(1):-

• Polarization is the condition where a more electronegative atom attracts the shared pair of electrons towards itself in a sigma bond

• The electron cloud becomes denser towards the more electronegative atom (In this case, Chlorine)

Polarization(2):-

• If this happens only between two atoms which owns lone pairs, the donator of the electron pair must submit to the will of the electronegative atom having no other go developing a partial positive charge on itself.

When more two atoms are involved

• In this case however, there is another carbon attached by sigma bond to the reference carbon.

• So now when Chlorine pulls away the lone pair of electrons from the reference Carbon, it now has another source (The second carbon) to rely on to reduce its positive charge on itself unlike the last case where it was alone.

Many Carbons getting polarized

• Therefore the reference Carbon pulls away its adjacent carbon's lone pair of electrons towards itself to reduce its positive charge intensity to some extent,

• Thereby a partial partial charge on the adjacent carbon is developed. This is the essence of inductive effect.

It can be guessed that this effect will continue for several adjacent atoms in the chain if present. This is the essence of INDUCTIVE EFFECT. It is a permanent phenomenon.

Definition of Inductive effect (Petition to remove)

• The phenomenon wherein an electron-releasing or an electron-withdrawing species is introduced to a chain of atoms the corresponding opposite charge is relayed through the chain by the atoms belonging to it.

Multiple Choice

What is inductive effect?

• Polarization between two atoms

• The phenomenon wherein a group's charge is relayed through a chain of atoms

• The phenomenon of Development of charge over multiple atoms due to same electronegative/ electropositive group

Multiple Choice

Is Inductive effect a permanent phenomenon?

• Yes

• No

+I and -I effects

• Inductive effect developed due to an electron donating group is called +I (Positive Inductive) effect. This distributes an equivalent negative charge on the chain of adjacent atoms

• Inductive effect developed due to an electron withdrawing group is called -I (Negative Inductive) effect. This distributes an equivalent positive charge on the chain of adjacent atoms

Properties of Inductive effect (1)

More electropositive/electronegative the functional group is, more the inductive effect is. This can be understood with the examples of +I and -I groups in the next slide.

Examples of -I groups

• Electronegative groups such as Halogens(-F, -Cl, -Br, -I) , -NO₂ (Nitro) , CN (Cyanide), -SO₃H (Sulphonic Acid) , Benzene ring (C₆H₅) , NH₂ (Ammine) , OH (Hydroxyl Group) , Carbonyl Groups (CO , CHO) , Carboxyl group (COOH)

• For Example, -I effect of CN > F

Examples of +I groups

Electropositive groups such as -R (All Alkyl groups), -COO^-,-O^-.

Order by decreasing effect:-

-O^- > -COO^- > R (Tertiary> Secondary > Primary > Methyl)

This is also the electropositive order of the groups.

^

Properties of Inductive effect (2)

• Inductive effect is additive in nature. For example +I effect of Tertiary butyl group > secondary carbon alkyl group.

• (Change image to support idea)

Carbocation stability(1)

Inductive effect is the same reason for the stability of carbocations. If the positive charge on the carbon is decreased in magnitude by induction, then that carbocation will be relatively more stable.

This is also the reason why SN1 reaction proceeds with much ease with tertiary alkyl groups

Carbocation stability(2)

If an electron withdrawing group is present, the positive charge of the sp² carbon is further intensified and the carbocation is destabilized.

Properties of Inductive effect (3)

• The intensity of the inductive effect diminishes for each consecutive carbon as the length of carbon chain increases i.e there is a greater number of atoms for dispersion of same charge as we increase the carbon chain length

• The effect usually becomes negligible after the third carbon in the chain

Multiple Choice

Which kind of inductive effect is exerted by the benzyl group on the alkane chain?

CH₃-CH₂-CH₂-C₆H₅

• +I effect

• -I effect

Multiple Choice

Which group has the highest -I effect?

• Br

• F

• Cl

• I

Multiple Choice

Assertion: Primary Carbon alkyl group exhibits higher +I effect than Secondary Carbon alkyl group.

Reason: Shorter chain length exhibits higher +I effect.

• Assertion is TRUE, Reason is TRUE, Reason is the correct explanation for Assertion.

• Assertion is TRUE, Reason is TRUE, Reason is NOT the correct explanation for Assertion.

• Assertion is TRUE, Reason is FALSE

• Assertion is FALSE, Reason is FALSE

Multiple Select

Which of the two following groups will exhibit the highest -I effects when attacked to an alkyl group (Highest Two)? (MULTIPLE OPTIONS CORRECT)

• -NO₂

• -CN

• -F

• -H

Multiple Choice

Arrange the following groups in the order of decreasing (+I) effect.

• a) C₆H₅O– > COO– > CR₃ > CHR₂ > H

• b) C₆H₅O– > H > CR₃ > CHR₂ > COO–

• c) CR₃ > C₆H₅O– > H > COO– > CHR₂

• d) C₆H₅O– > COO– > CHR₂ > CR₃ > H

Multiple Choice

Assertion: Secondary carbon alkyl group exhibits higher +I effect than Methyl group.

Reason: Inductive effect exhibits Additive property.

• Assertion is TRUE, Reason is TRUE, Reason is the correct explanation for Assertion.

• Assertion is TRUE, Reason is TRUE, Reason is NOT the correct explanation for Assertion.

• Assertion is TRUE, Reason is FALSE

• Assertion is FALSE. Reason is FALSE

Definition of Acids and Bases

• By Bronsted-Lowry definition of acids and bases, the one which donates H+ ion is an acid and the one which accepts H+ ion is a base.

Inductive effect (Acid-Base influence)

• If inductive effect can stabilize the compound after losing H+, then it is a strong acid by definition, else it is a weak acid (stronger base)

• For example, the given compound is stabilized by dispersing the resulting negative charge on the oxygen atom via -I effect of Cl group

Relative Stabilities of Acid and Bases

• In the first compound, due to -I effect, the negative charge on Oxygen atom is dispersed (intensity is reduced) hence stabilizing it and making it a strong acid (The one which can donate H+ easily)

Relative Stabilities of Acid and Bases

• However in the second compound, due to +I effect, the negative charge on the Oxygen atom is intensified (Destabilizing it) and making it a weak acid (Stronger base - the one which cannot donate H+ easily, rather accept it easily)

Multiple Choice

Is Chloro- Acetic acid a stronger acid than Acetic Acid?

• Yes

• No

Multiple Choice

Which is the most stable carbocation out of the following?

• CH₃CH₂C⁺HCH₃

• CH₃CH₂CH₂C⁺H₂

• C⁺H₃

• (CH₃)₂C⁺CH₃

CONGRAULATIONS! You have completed Part 1/3 of the course!

Now relax and click next to start next topic!

Steric Hinderance

Things are going to get crowded in here...

Steric Hinderance

• 'Steric' means spatial arrangement of atoms in a molecule. (explaination) Hinderance due to spatial arrangement of atoms in a molecule is called Steric Hinderance

Steric Hinderance

• When a Nucleophile (Electron Rich group) is hindered from reaching its reaction site due to a bulky group, say, methyl group contributing to a repulsive electron cloud over the region. This alters the rate of reaction in different alkyl groups during a SN2 reaction.

• This ultimately reduces the probability of that particular reaction from happening for each encounter of the nucleophile to the compound

In determining Acid-Base properties (1)

Due to steric hinderance, the site which has the ability to take a hydrogen ion can become unreachable, hence leading to less basicity than expected.

In determining Acid-Base properties (2)

Some compounds acid-base property depends upon how well its conjugate is stabilized by the solution it is in. If the site in question has steric hinderance, its acidity/basicity property is altered.

Multiple Choice

Lets revise what we have learnt!

Steric Hinderance is caused by?

• Overcrowding of Nucleophiles

• Hinderance due to Nucleophile

• Electron cloud repulsion due to a compound's spatial arrangement

• Presence of too many groups of same kind

Multiple Choice

Assertion: SN2 Reaction hardly proceeds with tertiary alkyl groups.

Reason: Tertiary carbocation is efficiently stabilized by inductive effect.

• Assertion is TRUE, Reason is TRUE, Reason is the correct explanation for Assertion.

• Assertion is TRUE, Reason is TRUE, Reason is NOT the correct explanation for Assertion.

• Assertion is TRUE, Reason is FALSE

• Assertion is FALSE Reason is FALSE

Multiple Choice

Given is a 3-D Ball-Stick model of tri-(TertiaryButyl)Amine. Why do you think an electrophilic attack is difficult here?

• Amines are noble in nature

• It is stabilized by induction

• The Electron rich center is sterically hindered

• There is a good chance that an electrophilic attack will occur.

Multiple Choice

Tertiary amine is more acidic than Secondary amine in water, though by inductive effect secondary amine must be more acidic than tertiary amine. Why is this the case?

• Too much inductive effect causes instability

• Tertiary amines are unstable

• The amine position cannot accept H+ ions due to steric hinderance

• Due to steric hinderance the amine cannot release much -OH group as its secondary counterpart

• Given statement is wrong. Secondary amine is actually more acidic than Tertiary amine in water.

CONGRATULATIONS! You have completed 2/3 of the course!

Click next to proceed to next topic!

Hydrogen Bonding

Dipole-Dipole interaction could use an upgrade!

Hydrogen Bonding

• Hydrogen bonding is a special type of dipole-dipole interaction involving a hydrogen atom located between a pair of other highly electronegative atoms

• Such a bond is weaker than ionic bond or covalent bond but stronger than any van der Waals interactions.

Hydrogen bonding in boiling point

Hydrogen bonding increases the number of bonds to overcome while boiling (Higher energy is required to boil such an aggregate)

This is the reason why Propanol has a higher boiling point than Chloropropane since the latter one cannot form hydrogen bonding

Here is an image of hydrogen bonding aggregate of many Methanol Molecules

Hydrogen bonding in solubility

Compounds which are capable of hydrogen bonding are highly soluble in hydrogen bonding solvents

Ethanol is highly soluble in water since it can form hydrogen bonding between water and itself.

Multiple Choice

What type of bond is hydrogen bonding?

• Co-Valent

• Partial-Ionic

• Van Der Waals Interaction

• dipole induced dipole interaction

Multiple Choice

Iodo Butane has a drasically lower boiling point despite its higher molecular weight than Butanol. What could be the reason?

• Iodo Butane is Highly Unstable

• Butanol has more number of atoms

• Butanol can form Hydrogen bonding

• Iodine molecules always have lower boiling point

Multiple Choice

Propane is not soluble in water. However Propanol is soluble in water to some extent. What could be the accurate reason?

• Like dissolves like

• Propanol is capable of forming hydrogen bonds with itself

• Propanol is capable of forming hydrogen bonds with water

• Propane cannot dissociate like Propanol does

Multiple Choice

An alcohol in water depends on its conjugate stabilization for its acidity. What could be the stabilizing factor here?

• H+ Ions released by water can surround the O- of the conjugate

• Water reacts with conjugate to restore the acid

• Water can form hydrogen bonding with the conjugate

• Water can create a shield over the conjugate via hydrogen bonding

Types of Hydrogen bonding (1) - Inter

When hydrogen bonding takes place between different molecules of the same or different compound, it is called intermolecular hydrogen bonding.

Intermolecular hydrogen bonding examples: water, para nitrophenol, alcohol

Types of Hydrogen bonding (2) - Intra

The hydrogen bonding which takes place within a molecule itself is called intramolecular hydrogen bonding.

Examples: ethylene glycol (C2H4(OH)2),ortho nitrophenol

Multiple Choice

What is the type of interaction experienced in glycols?

• Intra molecular dipole dipole interaction

• Intra Molecular Hydrogen bonding

• Inter Molecular Hydrogen Bonding

• Vicinal Diol special Dipole dipole interaction

Multiple Choice

Assertion: 2 Hydroxy Benzoic acid has lower boiling point than 4 hydroxy Benzoic acid.

Reason: 4 hydroxy Benzoic acid forms Hydrogen bonding with others of its kind, the former one forms Intra molecular hydrogen bonding

• Assertion and Reason BOTH are TRUE, Reason is the correct explanation for assertion

• Assertion and Reason BOTH are FALSE,

• Assertion and Reason BOTH are TRUE, Reason is NOT correct explanation for assertion

• Assertion is TRUE Reason is FALSE

• Assertion is FALSE, reason is TRUE

Hydrogen bonding - Viscosity

• Liquids whose molecules are polar or can form hydrogen bonds are usually more viscous than similar nonpolar substances.

• Honey, glucose and fructose are good examples of liquids which owes its viscosity to hydrogen bonding.

Hydrogen bonding - Surface Tension

• When many water molecules form hydrogen bonds with other water molecules, they form a lattice of water molecules, which is strong and flexible. This creates a high surface tension.

Hydrogen Bonding - Density

• When water freezes, water molecules form a crystalline structure maintained by hydrogen bonding. Solid water, or ice, is less dense than liquid water.

• Ice is less dense than water because the orientation of hydrogen bonds causes molecules to push farther apart, which lowers the density.

Multiple Select

Which of the following can be reasoned with hydrogen bonding?

• High Viscosity of Honey

• Ice being less dense than water of same volume

• Water having relatively higher surface tension

• Stabilization of Alcohol conjugate in water

• Higher boiling point of butane than propane

CONGRATULATIONS! You have completed 3/3 of the course!

It will be nice if we sharpen our skills!

Challenge round!

10 burning questions! Are you ready? Lets do it!

Challenge Round

Please read the question completely and understand it, then read through all options even if the first one seems the right one.

In Multiple Option Type Questions, there can be more than one correct answer, or just one correct answer.

All the best, lets proceed!

Multiple Choice

The decreasing order of acidity among

(I) phenol

(II) p-methylphenol

(III) m-nitrophenol

(IV) p-nitrophenol is

• I > II > III > IV

• IV > III > I > II

• III > IV > II > I

• IV > III > II > I

Multiple Choice

There exists a molecule with molecular formula KHF₂ . However KHCl₂ , KHBr₂ and KHI₂ does not exist despite seemingly belonging to same class. What could be the underlying reason?

• Flourine is highly electronegative than rest of the halogens hence its inductive effect is higher

• Flourine is highly electronegative enough to form Hydrogen bonds, other halogens cannot

• Flourine is incredibly small compared to other halogens

• Things just happen because they happen, screw this question

• There is a steric Hinderance with other molecules

Multiple Choice

Arrange the following in correct order of inductive effect of substituents

A) -NR₂

B) -OR

C) -F

• A > B < C

• A > B > C

• A < B < C

• A < B > C

Multiple Choice

Which contains the strongest Hydrogen Bond?

• O-_-H.....S

• S−H.....O

• F−H.....F

• S−H.....O

Multiple Choice

The pair of bases in DNA is held by which bond?

• Co-Valent bond

• Dipole-Dipole interaction

• Hydrogen Bond

• Deoxyriboic bond

Multiple Choice

HCl is a gas, but HF is a low boiling liquid. The reason could be

• H-F Bond is stronger

• H-Cl Bond is stronger

• Hydrogen Bonding can form compound aggregates

• H-F is a weak acid

Multiple Choice

Hydrogen Bonding is Maximum in

• Ethanol

• Diethyl ether

• Ethyl chloride

• Triethyl Amine

Multiple Select

What could be the stabilizing factors of Tertiary carbocation? (MAYBE more than one option correct)

• Hydrogen Bonding

• Inductive Effect

• Steric Hinderance

Multiple Select

Select all the correct statements given below (MAYBE more than one option correct)

• A Molecule capable of intra molecular hydrogen bonding will have a relatively higher boiling point

• Hydrogen bonding is responsible for viscosity of tar

• All 6 infinity stones hydrogen bonded to activate the gauntlet

• Tertiary Alkyl Halide will have the fastest SN1 Reaction rate

• Tertiary Alkyl Halide will have the fastest SN2 reaction rate

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