Organic Chemistry

Chapter 4: Alkanes & Cycloalkanes

Hydrocarbons—Compounds that are only composed of hydrogen carbon

Saturated Hydrocarbons—DO NOT contain any pi bonds

IUPAC System—International; Union of Pure and Applied Chemistry

Finding The Parent Chain

• Pick the parent chain with the most substituents

• If a parent chain is a cyclic (ring of carbons), you add the prefix “cyclo” to the beginning of the parent name

Identify Substituents (side groups)

• Number in sequence of consecutive carbons in a parent chain

• The number/locant is to communicate where each substituent is attached to the parent chain

• When counting the substituent DO NOT count the parent molecule

Branches With 3 Carbon’s

Branches With 4 Carbon’s

Branches With 5 Carbon’s

Rules To Follow When Numbering The Parent Chain

1. If one substituent is present, number the parent chain to give the substituent the lowest number possible

2. When you have multiple substituents are present, number the parent chain to give the first substituent the lowest number possible

3. If there’s a tie, then number the parent chain so that the second locant gets the lowest number possible

4. If there is no tie breaker, then assign the lowest number by alphabetically

5. Then assemble the complete name, assign a locant to each substituent, and lost them before the parent chain name in alphabetical order

6. A prefix is used if multiple substituents are identical

   • Di

   • Tri

   • Tetra

   • Penta

7. Prefixes are NOT used for alphabetical purposes, except for the prefix “iso”

Newman Projections

• Look directly down the C-C bond

• The front carbon should eclipse the single bond and the carbon behind it

• Show the front carbon as a point and the back carbon as a large circle behind it

Rotational Conformation

Cycloalkanes

• Cyclopropane—

  • angle strain

  • bond angles of 60 degrees cause electron pair repulsion in adjacent bond

  • inefficient sigma bond overlap

  • Torsional Strain—eclipsing C-H bonds all the way around the ring

• Cyclobutene—

  • angle strain results from bond angles of 88 degrees, although it is not as severe as the 60 degrees angles in cyclopropane

  • slight torsional strain results because adjacent C-H are neither fully eclipsed not fully staggered

• Cyclopentane—

  • angles are closer to the optimal value

Chapter 3: Acids & Base

Bronsted-Lowry Definition—

• Acid—Proton donor

  • Any chemical species that releases a hydrogen ion to another substance

• Base—Proton acceptor

  • Any chemical species-such as an ion or a molecule that can accept a hydrogen ion from another- substance during a chemical reaction

• Conjugate Acid—A conjugate acid results when a base accepts a proton

• Conjugate Base—A conjugate base results when an acid gives up a proton

Bronsted-Lowry Acidity: Quantitative Perspective

• $K_{a}$ —is the equilibrium constant for the reaction between an acid and water

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$K_{a}=\frac{\left\lbrack H_3O^{+}\right\rbrack\left\lbrack A^{-}\right\rbrack}{\left\lbrack HA\right\rbrack}$

$pK_{a}=-\log K_{a}$

• Lower pKa = stronger acid

• If pKa < 0 then complete dissociation in $H_2O$

  • H-Cl

  • H-Br

  • $H_2SO_4$ -HI

pKa Values of Common Compounds

• pKa—is a measure of the ability of a particular compound to donate its proton (H+)

• Strongest acids = Weakest conjugate

• Weakest acid = Strongest conjugate

Predicting the direction of acid/base equilibrium that is favored

• Compare acid

• Low pKa = Stronger acid

• Equilibrium favors the higher pKa which means its less likely to dissociate

• Higher pKa = harder to remove proton = more of it in solution

Bronsted-Lowry Acidity: Qualitative Perspective

• Qualitive Analysis—Compare structural stability to determine which is stronger acid

• Factors affecting stability of negative charge (ARIO)

  • Atom—electronegativity and size can stabilize a negative charge

  • Resonance—can greatly stabilize a formal negative charge by spreading it out into partial charges

  • Induction—stabilizes by withdrawing electron density from site of acidity through bonds (tug of war)

  • Orbital—stabilize negative charges by pulling electron density closer to the nucleus

Lewis Acids & Bases

• Lewis acid—accepts and shares a pair of electrons

• Lewis base—donates and shares a pair of electrons

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