c341 f2011 chapter 1 general chemistry...

C341 Fall 2011/Chapter 1

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Welcome to C341!! Chapter 1 & 2:

Review of General Chemistry What will we do today? 1. Review of the syllabus together.

2. Discuss course structure and textbook.

You will use the entire textbook between C341, C342 and C343.

3. Set realistic expectations for work load.

4. Start reviewing general chemistry concepts in chapter 1.


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Pertinent subjects in C117 that lead to success in C341:

1. Periodic table; charges on ions and atoms by group

2. Types of bonding; ionic versus covalent bonds, e.g. NaOCH3, NaH

3. Lewis structures; organic line drawings, understanding ball and stick drawings with wedges and dashes; bond polarity and molecular polarity; functional groups would be nice.

4. Hybridization, shape, and VSEPR.

5. Resonance structures with organic molecules, not just carbonate, sulfate and nitrate.

6. Intermolecular forces, physical properties and solubilities in water versus hydrocarbons.

7. Thermochemistry; bond energies, potential energy diagrams and enthalpy changes.

8. Kinetics; one‐step versus two‐step reactions, reaction mechanisms and their rate laws.

9. Equilibrium; equilibrium constants; Le Châtelier’s principle; product‐favored versus reactant‐favored.

10. Thermodynamics, ΔG and spontaneity; product‐favored versus

reactant‐favored.


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Chapter 1 & 2 outline:

1. Lewis Structures for organic compounds

Line Drawings ‐ drawing organic compounds

Formal charge

Resonance, resonance contributors & bond order

2. Bond Angles & Shapes

3. Hybridization

4. Bond Polarity & Molecular Polarity

Polar & Non‐polar compounds

5. Intermolecular forces

6. Predicting physical properties based on intermolecular forces

7. Predicting solubility based on intermolecular forces

Solubility of molecules

8. Functional Groups – may be new material for some people

You should do all the problems within the chapter and at the end of the chapter. But if you who want to do the minimal amount of work: Chapter 1: 1.34 (use line drawings), 1.39, 1.45, 1.46, 1.48, 1.52, 1.53, 1.56 (draw this as a line drawing), 1.61, 1.63, 1.64 Chapter 2: 2.43‐2.50, 2.53, 2.55‐2.58, 2.61, 2.63‐2.66


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1. Lewis Dot Structures from Condensed Structural Formulae

A Lewis Structure depicts the structure of a compound by its arrangement of atoms with its neighbors, bonds that exist, and the presence of lone pairs.

Molecules share electrons in order to achieve a closed shell or a total of 8 electrons surrounding each atom (octet rule).

Hydrogen is the only atom who is content with only 2 electrons.

Don’t forget that third row atoms or lower can exceed an octet, e.g. S and P.

CH3COCH2NH2

CH3CO2CHCHCH3

CH3CHOHCH2CONHCH2CH3


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Line Drawings Amoxicillin:

Estrogen (female steroid): Zingerone (pungent extract from ginger):

Capsaicin (you and a neighbor come up with the formula for this):


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Constitutional Isomers: Single bonds are axes of rotation to form conformers:

Constitutional isomers of hexanes:

Draw several constitutional isomers for C4H10O:


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Formal Charge

O SN

OOH

N


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Resonance Structures:

o Some molecules cannot be adequately represented by a single Lewis structure.

o Resonance structures are two Lewis structures having the same placement of atoms but a different arrangement of electrons.

o Resonance allows certain electron pairs to be delocalized over several atoms,

and this delocalization adds stability to the molecule. o A molecule with two or more resonance forms is said to be resonance

stabilized.

o Resonance structures are possible if electrons are in conjugation. Rule 1: All resonance structures must have the same number of valence e’s. Rule 2: The octet rule must be obeyed and not exceeded (esp. for C, O, N,& H). Rule 3: Nuclei do not change positions in space between resonance structures. Rule 4: Sigma bonds must not be broken and the skeletal structure rearranged.

Conjugation = A series of alternating single and multiple bonds with overlapping p orbitals.


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Organic Resonance structures (anions, cations & neutral compounds):

Recognizing allylic and vinylic positions:

Indicate all chlorides as either allylic and vinylic: Circle all the allylic lone pairs:

Cl

Cl Cl

Cl

Cl


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O

NH

O O


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Common Mistakes

Localized vs. delocalize electrons. Generally, lone pars adjacent to a C=C double bond are capable of resonance, but not in this case.

Your turn to practice with a neighbor:

O

N

N


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2. Bond angles & shapes VSEPR Theory predicts the MOLECULAR SHAPE & ANGLES FACT: Molecules bond such that all the regions of electron density around a central

atom are as far away from each other as possible.

Determine the shape, not geometry, for the following atoms:

N

O O

OO

cocaine


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3. Hybridization, σ & π‐bonds

Single bonds –

End‐to‐end overlap of orbitals of two ‘s’ orbitals.

Electron density is found along the bond axis in between the atoms.

The first bond between any 2 atoms is always a σ‐bond.

Multiple bonds –

Multiple bonds arise from a combination of a σ ‐bond and π–bonds.

π ‐bonds have their electron density above and below the bond axis.

π ‐bonds arise from the parallel overlap of unhybridized p orbitals.

π ‐bonds are weaker than σ‐bonds.

Two π ‐bonds on the same atom are made in perpendicular planes.


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Determine the hybridization for the following atoms:

Co-enzyme Q-10

H3CO

H3CO

O

O

Hybridization of an amide?


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Orbital overlap descriptions:


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4. Bond Polarity & Molecular Polarity

Electronegativity = The relative ability of an atom to attract electron density to itself during a covalent bond (expressed on a scale relative to “F” being assigned a number of 4.0)

Expressions of bond polarity


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Which of the following bonds are polar? How do we illustrate that a bond is polar and which direction is the electron density flowing?

H—Br C—O C—H O—H B—H C—I

Bond polarity relates to acidity in chapter 3:

H2B—H H3C—H H2N—H HO—H H—F


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Polar molecules versus non‐polar molecules

A. Use electronegativity values to predict bond dipoles (assign δ+ and δ ‐). B. Use the VSEPR method to predict the molecular shape. C. From the molecular shape, determine whether bond dipoles cancel to give a

non‐polar molecule or combine to produce a resultant dipole moment for the molecule.

Start to learn these organic solvents below (they will be tested on quiz 1/exam 1). Which are polar and non‐polar?

O

acetone

O

H N

DMF(dimethyl

formamide)

O

OHacetic acid

CH3

toluenehexanediethyl ether

S

O

DMSOdimethly sulfoxide

H3C C N

acetonitrilemethanol

CH3OH

O

O

THF(tetrahydrofuran)

methylene chlorideCH2Cl2


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Where do you draw the line between polar vs. non‐polar?

Dielectric constant = the property of a dielectric that determines the electrostatic energy per unit volume for unit potential gradient. WHAT does that mean?

What is considered a polar solvent based on dielectric constant?

Name Structure bp, oC dipole momentdielectric constant

water H‐OH 100 1.85 80

formic acid 100 1.41 58

diemthyl sulfoxide (DMSO) 189 3.96 47.2

N,N‐dimethylformamide (DMF)

153 3.82 38.3

acetonitrile 81 3.92 36.6

methanol CH3‐OH 68 1.70 33

ethanol CH3CH2‐OH 78 1.69 24.3

acetone 56 2.88 20.7

1‐propanol CH3CH2CH2‐OH 97 1.68 20.1

methyl ethyl ketone 80 2.78 18.5

1‐butanol CH3CH2CH2CH2‐OH 118 1.66 17.8

methylene chloride (DCM) CH2Cl2 40 1.60 9.08

tetrahydrofuran (THF) 66 1.63 7.52

acetic acid 118 1.74 6.15

ethyl acetate 78 1.78 6.02

diethyl ether CH3CH2OCH2CH3 35 1.15 4.34

benzene 80 0 2.28

carbon tetrachloride CCl4 76 0 2.24

hexane CH3(CH2)4 CH3 69 ‐‐‐‐ 2.02


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5. Intermolecular Interactions

Intramolecular forces (covalent & ionic forces) are strong.

Intermolecular forces are comparatively weak. But these intermolecular forces add up to make an “overall” significant contribution to the overall physical property of a substance.

Review the types of intermolecular forces: Relative strengths

o H‐bonding (HBA & HBD) 10‐40 kJ/mol o Dipole‐dipole forces (DD) 5‐25 kJ/mol o London dispersion forces (LDF) 0.5‐40 kJ/mol o Induced dipole 2‐10 kJ/mol

Compare to: Relative strengths

o Ionic 400‐4000 kJ/mol o Covalent 150‐1100 kJ/mol o Metallic 75‐1000 kJ/mol

Why is understanding intermolecular forces (IMF) important?

Solubility in solvents (hydrophobic vs. hydrophilic)

Physical properties like boiling and melting points (e.g. the stronger the

intermolecular forces the higher the boiling point)

Three dimensional structures (consider the tertiary structure of a protein)

Reactivity between species


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Non‐polar molecules tend to experience predominately:

London Dispersion Forces (a.k.a. van der Waals forces) WEAK, attractive forces between molecules with TEMPORARY DIPOLE. What dictates extent of LDF?

What is polarizability? Which are more polarizable: cations or anions? Compare the isomers of hexane – they have the same number of atoms and electrons. Which has higher LDF and why?


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Polar organic molecules tend to experience:

Dipole‐dipole forces: attractive forces between molecules with a PERMANENT DIPOLE. Demonstrate how acetone exhibits a DD interaction (you must understand polar bonds and dipoles first).

H‐bonding: an especially strong dipole‐dipole attraction forces between molecules that have X—H bonds (X = O, N, F only). What are HBA and HBD? Demonstrate an H‐bonding interaction:


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6. Predicting physical property trends in organic chemistry

Work with your neighbors to put the following compounds in order of boiling point.

Also put in an example of the methyl butyl amine.


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7. Polarity Effects on Solubility (“Like dissolves like”)

Which would you predict to be soluble in water?

Which would you predict to be NOT water soluble?

Which are protic?

Which are aprotic?

O

acetone

O

H N

DMF(dimethyl

formamide)

O

OHacetic acid

CH3

toluenehexanediethyl ether

S

O

DMSOdimethlysulfoxide

H3C C N

acetonitrilemethanol

CH3OH

O

O

THF(tetrahydrofuran)


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What type of solvent would you use to dissolve cholesterol? (Ask me now about the 5‐carbon rule…)

Micelles:

HO

H

H

H

cholesterol


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Predict the solubility of the following molecules:

NHO

HO OH

NH2

ON

O

Vitamin B6 Novocain (procaine)

OO OH

OH

HO OH

O

O

5

Vitamin C Vitamin K

O

HO

HO Vitamin E Vitamin D

O N

Cl

N

H3CHN Cl

Cl

Valium (diazepam) Zoloft – antidepressant


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8. Functional Groups:

Organic Chemistry is the study of carbon and the compounds that contain carbon (also contain H, N, O & S)

Organic compounds are organized by classes called functional groups.

A functional group is an atom or a group of atoms with characteristic chemical and physical properties. It is the reactive part of the molecule.

The different functional groups refer to compounds that have similar properties with similar chemical bonds.

Functional groups differ based on their component heteroatoms or pi‐bonds.

Heteroatoms have lone pairs and create electron‐deficient sites on carbon.

Many molecules have several functional groups in one molecule!

Capsaicin:


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Hydrocarbons

Hydrocarbons contain carbons and hydrogens; generic formula of R—H (ask me what the R means).

Functional group

Characteristic Examples

Alkanes Contains all C—C single bonds

Alkenes Contains at least one C=C double bond

Alkynes Contains at least one C≡C triple bond

Arenes Contains at least one benzene ring

CH3

NO2

NO2O2N

CH3

Toluene

TNT = trinitrotoluene

Naphthalene = moth ballsOH

NO2

NO2O2N

OH

Phenol

Picric acid = insecticide


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FG Characteristic Examples

Alcohol R—OH

Primary (1o) Secondary (2 o) Tertiary (3 o)

Thiol R—SH


Ether R—O—R

Thioether R—S—R

SSAmines R—NH2


Nitriles R—C≡N

Alkyl Halides

R—X, X = halogen



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Carbonyl containing compounds: C=O is called a “carbonyl group”

RC

O

H RC

O

R Aldehyde Ketone

RC

O

OH RC

O

OR RC

O

NH2

Acid chloride Carboxylic acid Ester Amide

Identify correct functional groups in the following molecules.


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Working with a neighbor/after class, determine the following: Functional groups? Soluble (S) or insoluble (N) in water?

IMF? LF (London Forces), DD (dipole‐dipole), HBA (hydrogen bond

acceptor), and HBD (hydrogen bond donor) as appropriate.

CH3

OHO

O

OH

S or N S or N S or N S or N

LF LF LF LF

DD DD DD DD

HBA HBA HBA HBA

HBD HBD HBD HBD

NH

N

O

O

O

S or N S or N S or N S or N

LF LF LF LF

DD DD DD DD

HBA HBA HBA HBA

HBD HBD HBD HBD

c341 f2011 chapter 1 general chemistry...

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