Organic Chemistry I - EXAM II: HOMEWORK/REVIEW

Write the name of five +I groups.

+I NH4+: Ammonium group H3O+: Hydronium group C2H3+: Vinyl group CH3+: Methyl group C3H5+: Allyl group

Write the name of five -I groups.

-I NH2-: Amino group OH-: Hydroxyl group CHO-: Carbonyl group NO2-: Nitro group HSO3-: Sulfonic group

Identify the correct relationship: 1) pH = - log [H3O+] 2) pH = - log [OH-] 3) pH = log [H3O+] 4) log [OH-] (e) NOTA

1

Name 3 tribasic bases:

1) Al(OH)3 2) Ga(OH)3 3) In(OH)3

Name 4 dibasic bases:

1) Ca(OH)2 2) Sr(OH)2 3) Mg(OH)2 4) Ba(OH)2

Name 7 monoprotic acids

1) HNO3 2) HCl 3) HBr 4) HI 5) HCOOH 6) CH3COOH 7) CF3COOH

Name 4 monobasic bases:

1) LiOH 2) NaOH 3) KOH 4) CsOH

34. According to Baeyer's Strain Theory the angle strain in cyclopentane is ___________ whereas that of cyclohexane is ___________.

1, -11

Write the postulates of Baeyer's Strain Theory.

1. All cycloalkanes are Co-planar because the atoms present in any cycloalkane molecule lie in the same plane. C-C angle is 109°28' 2. The deviation of bond angle from the normal tetrahedral angle is called angle strain 3. The greater the angle strain, the greater the instability of ring 4. The higher the stability of the ring the greater would be its ease of formation

Arrange and justify the order of acidic strength of the following compounds: Chloroacetic acid, Fluoroacetic acid, Dichloroacetic acid, and Trichloroacetic acid.

1. Chloroacetic acid 2. Fluoroacetic acid 3. Dichloroacetic acid 4. Trichloroacetic acid - The stronger electron withdrawing group the more stable the conjugate base so the stronger the acid will be. Fl is more electronegative and a stronger WG (withdrawing group) than Cl. Multiple EWG increases the acidity more than a single group.

What is the approximate range of the acidity constant, Ka?

10^15 - 10^-60

The value of pH + pOH is equal to

14

The pKa of water is________

15.74 and considered standard

Arrange the following five compounds with the increasing order of acidity:

2 1 5 3 4

The IUPAC name of Isobutane is _________________

2-Methylpropane

The compounds represented by the structures are: 1) Structural isomers. 2) Identical. 3) Cis-trans isomers. 4) Conformers. 5) Constitutional isomers.

3) Cis-trans isomers.

How many different types of strains are possible in a molecule?

3, angle, torsional, steric

Consider this chair conformation: When the ring flips, 1) the chlorine becomes axial and the ethyls become equatorial. 2) all three substituents become equatorial. 3) the chlorine becomes equatorial and the ethyls become axial. 4) the ring opens up. 5) one ethyl becomes axial, one becomes equatorial, and the chlorine becomes equatorial.

3: the chlorine becomes equatorial and the ethyls become axial.

The CH3—CH3 (eclipsed) torsional strain is ___________ kJ/Mol whereas the CH3—CH3 (gauche) torsional strain is ____________ kJ/Mol.

4.0, 3.8 none of the above

The H—H (eclipsed) torsional strain is _______ kJ/Mol whereas the H—CH3 (eclipsed) torsional strain is__________ kJ/Mol.

4.0, 4.0

According to Baeyer's Strain Theory the angle strain in cyclopropane is ___________ whereas that of cyclobutane is _____________

49, 19

What is the dihedral angle between Ha and Hb (see below)? (a) 0° (b) 30° (c) 60° (d) 120° (e) 180°

60°

What do you mean by conjugate acid and conjugate base? Explain with suitable example (equation is to be given).

A conjugate acid, within the Brønsted-Lowry acid-base theory, is a species formed by the reception of a proton (H+) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is merely what is left after an acid has donated a proton in a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.

Al(OH)3 is a Brønsted base but Lewis acid —Explain.

According to the Brønsted-Lowry theory: an acid only exists as such in relation to a base, and vice versa. Al(OH)3 + OH− ⇌ Al(OH)−4 acting as an acid: loses H+ to become OH−. 3H+ + Al(OH)3 ⇌ 3H2O + Al3+(aq) acting as a base: gains H+ to become 3H2O+

Draw and explain the Eclipsed and Staggered conformation(s) of Ethane.

An eclipsed conformation is the highest energy, least stable conformer where all 6 C-H bonds are as close as possible to each other. A staggered conformer is the lowest energy, most stable conformer and all C-H bonds are as far away as possible.

The formation of hydronium ion is a ________ acid-base reaction.

Arrenhius

Except proton, Brønsted acids are not Lewis acids — Justify.

Bronsted acids are not Lewis acids because they cannot accept an electron pair directly (only a proton would be a Lewis acid)

Why was Baeyer's theory incorrect?

Baeyer assumed that all cycloalkanes are flat (most adopt a puckered 3-D conformation), he also did not consider the contribution of torsional strain to the overall strain energy of a molecule

Aluminum hydroxide (Al(OH)3) is amphoteric in nature — Justify (equations need to be given).

Because Aluminum hydroxide can be both an H+ donor and receiver it is amphoteric

Benzoic acid is stronger acid than acetic acid— Explain:

Because the benzoate ion resulted from Dissociation of Benzoic acid is stabilized by resonance whereas the Acetate ion resulted from Dissociation of Acetic acid IS NOT stabilized.

2,4,4-trimethylheptane

C10H22

4-ethyl-3,4-dimethyloctane

C12H26

3,3-diethyl-2,5-dimethylnonane

C15H32

What is the structure of Isobutane?

C4H10

What is the structure of N-Butane ?

C4H10

Trans-1,2-diethyl cyclopropane

C7H14

The compounds n-Butane and Isobutane are ___________ isomer whereas Ethyl alcohol and Dimethyl ether are ______________ isomer.

Constitutional, Functional

The ____________ ring looks like an envelope.

Cyclopentane

Explain torsional strain in a molecule.

Eclipsing of bonds on neighboring atoms

Electromeric effect is seen in ________ π system whereas resonance effect predominates in __________ π system.

Electromeric effect is a temporary effect and takes place between two atoms joined by a multiple bond, i.e., a double or triple bond. It occurs at the requirements of the attacking reagent, and involves instantaneous transfer of a shared pair of electrons of the multiple bonds to one of the linked atoms. It is denoted as E effect. Resonance is a hypothetical concept in which molecule is represented by more than one form called canonical form or resonating structure and the property of the molecule is represented by combination of all canonical forms called resonance hybrid.

Explain angular strain in a molecule.

Expansion or compression of bond angles away from the preferred 109.5°28'

What relationship does this portray? (a) Gauche (b) Anti (c) Peri (d) Eclipsed (e) Staggered.

Gauche

Field effect

Gen Chem did not cover

Name 1 diprotic acids

H2SO4

Name 1 triprotic acids

H3PO4

Arrange the following acids according to the decreasing order of acidity: HF, HBr, HI, HCl

HI (strongest), HBr, HCl, HF (weakest)

Arrange the following acids according to decreasing order of acidity: Hypoiodous acid, Hypobromous acid and Hypochlorous acid.

HOCl (Hypochlorous acid) *Strongest > HOBr (Hypobromous acid) > HOI (Hypoiodous acid) *Least acidic

Why is CH3COOH stronger acid than HOH?

HOH (H2O) is a weaker conjugate acid, making it a stronger base and CH3COOH is a stronger conjugate acid making it a weaker base.

In cyclobutane the bend ________ angle strain but ___________ torsional strain.

Increases, Decreases

Arrange the relative strength of the following factors on acidity (structural effects) of a molecule: Resonance, Atomic radius, Electronegativity, Inductive effect.

Inductive effect, Electronegativity, Atomic radius, Resonance

Hi is more acidic than HF — Explain.

Iodine is so much bigger than fluorine that the charge is more stable on this larger atom. Thus, the trends for acidity of the hydrohalic acids are as follows: HI is strongest, followed by HBr, HCl, and finally HF.

The co-ordination of water with metal ion is a ________ acid-base reaction.

Lewis

The interaction of Fe2+ in heme with O2 is a ________ acid-base reaction.

Lewis

The transition metal salts, such as TiCl4, FeCl3, ZnCl2, and SnCl4 are

Lewis acids

A significant similarity between acetone, acetaldehyde, ethyl alcohol, acetic acid, acetyl chloride and acetamide is, all of these compounds are:

Lewis base

Boron trifluoride-etherate can be considered as:

Lewis base

rrange the following molecules according to increasing acidic order: Hydrofluoric acid, Methane, Water and Ammonia— Explain your predicted order.

Methane < Ammonia < Water < Hydrofluoric acid

Draw the conformations of (i) Cis-decalin (ii) Trans-decalin and (iii) the most stable shape of decane.

Most stable is Trans-decalin

Arrange and justify the order of acid strength of the following molecules: O2NCH2COOH, FCH2COOH, CICH2COOH, BrCH2COOH, ICH2COOH, CH3COOH, (CH3)2CHCOOH.

O2NCH2COOH > FCH2COOH >CICH2COOH > BrCH2COOH> ICH2COOH > CH3COOH Reason : Acidic strength decreases as -I effect of the group or halogen decreases.

Explain with appropriate equations (at least two) why water is called amphoteric?

Referring to the Bronsted Theory, an acid is an H+ donor and a base is the one that accepts the H+ . Because water can do both it is therefore amphoteric.

explain steric strain in a molecule.

Repulsive interactions between nonbonded atoms in close proximity. Repulsive interaction occurring between atoms that are forced closer together than their atomic radii allow. In other words, repulsive interactions when two atoms or groups bump into one another.

Methanesulfonic acid (pKa = -1.2) is stronger acid than acetic acid (pKa = 4.74) — Explain.

The acetate ion shares the negative charge with 2 O atoms and the Methanesulfonic ion has a negative charge spread over 3 O atoms, this delocalization help stabilize the anion.

How can you explain the acid strength of Hypochlorous acid, Chlorous acid, Chloric acid and Perchloric acid?

The acid strength increases as the number of oxygen atoms increase. The number of oxidation will increase in Cl.

Arrange and justify the order of acidic strength of the following compounds: Butanoic acid, 2Chlorobutanoic acid, 3-Chlorobutanoic acid, 4-Chlorobutanoic acid.

The closer the Cl gets to the COOH, the stronger the acid. By adding an electron withdrawing group such as -Cl, this stabilizes the conjugate base resulting in a strong acid. The magnitude of the inductive effect depends on the number of bonds between the ewg and the size of the negative charge. 1. Butanoic acid 2. 4-Chlorobutanoic acid 3. 3-Chlorobutanoic acid 4. 2Chlorobutanoic acid

What do you mean by the flipping of a cyclohexane ring?

The exchange of axial and equatorial positions caused by an inter-converted chair conformation.

Draw and explain the Sawhorse and Newman projection(s) considering Ethane as an example.

These conformations are the arrangement of atoms resulting from bond rotation. Sawhorse projects allow you to view C-C bonds from an oblique angle and indicate spatial orientations by showing all the C-H bonds *(you can see ALL C-H bonds). Newman projections only allow the visibility of ONE C bond.

Inductive effect

Transfer of charge (electron withdrawal or donation) through a chain of atoms in a molecule by electrostatic induction.

Comparing CF3SO3H (Trifluoromethanesulfonic acid) and CH3SO3H (Methanesulfonic acid), which has the higher pka? Why?

Trifluoromethanesulfonic acid is a stronger acid. When you compare the strengths of the conjugate bases, the weaker the base, the stronger the conjugate acid. In the case of the trifluoro derivative, the presence of the highly electronegative fluorine atoms serves to delocalize the negative charge to a greater extent. This additional delocalization makes trifluoromethanesulfonate a weaker base.

A solution in which [H+] > [OH-] is _______ whereas a solution in which [H+] < [OH-] is _____

acidic, basic

Because of the flipping of a cyclohexane ring the __________ hydrogens become ________ and the __________ hydrogens become _____________

axial, equatorial and equatorial, axial

Hyperconjugation is also known as no ___________ resonance.

bond

Isopropylamine and Propylamine are ______________ isomers.

constitutional

In cyclopropane all C—H bonds are _________

eclipsed

Inductive effect is a _________ effect whereas electrometric effect is a _________ effect.

electron density, polar rise

The pH of an acidic solution is ________ than _______ whereas for an alkaline solution________ than _______

lower than 7, higher than 7

In general, equatorial positions give more __________ isomer.

stable

What do you mean by 1,3-diaxial interactions? Explain with a suitable diagram.

the steric interaction between axial substituents bound to carbon atoms in a six-membered ring, resulting in a steric destabilization