CSUMB
ESSP 311 Organic Chemistry I
Ronald W. Rinehart, Ph.D.

Chapter 1 Chemical Bonding

Blackwell's "11th Hour" tutorial on structure, bonding, and properties
http://www.blackwellpublishing.com/11thhour/book6/oc1ch1.html
http://www.blackwellpublishing.com/11thhour/book6/index.html > Chapter 1
Dr. Robert Wiley's tutorial on bonding and isomerism
 http://www.amug.org/~rwiley/Organic_Chemistry_Site/bonding_and_isomerism.htm
Organic Chemistry Online by Paul R.Young at the University of Illinois at Chicago
 Structure and Bonding tutorials  
[requires MDL Chime; use Netscape]

http://www.chem.uic.edu/web1/OCOL-II/WIN/STRUCT.HTM
From Oxford University, there is a really good tutorial on chemical bonding in organic molecules, based on Foundations of Chemistry by Richard E. Dickerson and Irving Geis.
[requires MDL Chime; use Netscape]
 go to:   http://www.chem.ox.ac.uk/vrchemistry/orbitals/html/page01.htm 
Carey PowerPoint slides for chapter 1 [1.1 to 1.6, atoms, orbitals, bonds, polarity, formal charge] from Columbia University can be seen at
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_01_06.html
Carey PowerPoint slides for chapter 1 [1.7 to 1.9, structural formulas, constitutional isomers, resonance] from Columbia University can be seen at
 http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_07_09.html
Carey PowerPoint slides for chapter 1 [1.10 to 1.11, molecular shapes, molecular dipole moments] from Columbia University can be seen at
 http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_10_11.html
Carey PowerPoint slides for chapter 1 [1.12 to 1.14, electron waves, bonding, VB and MO models] from Columbia University can be seen at
 http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_12_14.html
Carey PowerPoint slides for chapter 1 [1.15 to 1.19, hybridization and bonding] from Columbia University can be seen at
 http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_15_19.html
A set of 154 PowerPoint slides on structure and bonding in PDF format
by Paul R. Young of the University of Illinois at Chicago can be seen at
http://www.chem.uic.edu/web1/PDF/CH1.PDF
You will need both Adobe Acrobat Reader 4.0 and Apple's QuickTime to view these presentations
Introduction to organic chemistry [including chemical bonding]
by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/introtoorgchem.htm

Chapter 1.  Chemical Bonding 
    I.  Review of Orbitals and Bonding
 
            A. Orbitals 
                        1. Orbitals represent probability regions of high electron density about the nucleus. 
                        2. Atomic orbitals can be s, p, d, f
                        3. Valence electrons are electrons in the outermost energy levels. 
                        4. Electrons of an atom can be described in terms of its electron configuration. 
                        5. Atoms and ions tend to be most stable in a noble gas configuration (an "octet"). 
                                    a) Ionization energy.
                                                Na.  +   energy ---->  Na+  +  e

                                    b)         Electron affinity.
                                                Cl +  e-  ---->  Cl¯  +  energy 

            B. Bonding. 
                        1.  Ionic Bonds:  Electron transfer.    
                                    a)  Metal - Nonmetal 
                                    b)  Example:  NaCl 
                                         Na  1s22s22p63s1                  Cl   1s22s22p63s23p5 
                                         Na+ 1s22s22p6                      Cl-  1s22s22p63s23p6 

                         2.  Covalent Bonds:  Sharing of electrons. 
                                    a)  Nonmetal - Nonmetal or
                                         Nonmetal - Metalloid 
                                    b)  Nonpolar Covalent Bonds-  Equal (or nearly equal) sharing of electrons. 
                                        The two bonding atoms have equal (or nearly equal) electronegativities: 
                                            less than 0.5 units difference in electronegativity.
                                    c)  Polar Covalent Bonds-  Unequal sharing of electrons:  greater than 0.5
                                                 units difference in electronegativity
                                                i)  Classify the following bonds: 
                                                    C-H     O-H     C-O     Mg-I  
                                    d)  Dipole moment: 
m = e ∙ d
                                                where e is the charge in esu (electrostatic units), d is the
                                                distance separated in cm, and
m is the dipole moment in Debyes. 

                        3.  Hybridization

see the Hybrid Orbital Tutorial at Colby College [you need Shockwave™]
http://www.colby.edu/chemistry/OChem/DEMOS/Orbitals.html

 Raymond Chang's Hybrid Orbital Flash Movies  
  http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/hybrv18.swf  

              Atomic Orbitals at Purdue University  
http://www.chem.purdue.edu/gchelp/aos/index.html  

                                    a)  sp3 hybrids:  CH4  C2H6 
                                                i)   109.5o bond angles 
                                                ii)   25% s character 
                                                iii)   sigma bonds
                                                iv)   tetrahedral  

                                    b)  sp2  hybrids:  CH2=CH2 
                                                i)  120o bond angles 
                                                ii)  33.3% s character 
                                                iii)  sigma bonds and pi bonds 
                                                iv)  trigonal planar center    
                                    c)  sp  hybrids:  HC≡CH 
                                                i)   180o bond angles 
                                                ii)   50% s character 
                                                iii)  sigma bonds and pi bonds 
                                                iv)  linear  
                        4.  Molecular Orbitals 
                                    a)  Combinations of atomic orbitals result in molecular orbitals. 
                                    b)  In-phase overlap of atomic orbitals result in bonding molecular orbitals. 
                                    c)  Out-of-phase overlap of atomic orbitals   result in antibonding molecular orbitals. 
                                    d)  End-to-end overlap of s, sp, sp2, sp3 results in sigma
(s) bonds. 
                                    e)  Sideways overlap of p-orbitals results in pi 
(p) bonds. 
                                    f)  Examples:  H2
        H2-         He2              O2    O2+   O2- 

II.        Lewis Structures. 

See Colby College's Shockwave tutorial "Representing Compounds"
 http://www.colby.edu/chemistry/OChem/DEMOS/Repcmpds.html

See the page on Lewis Structures by Brenda Wojciechowski and Paul Cerpovicz
at Georgia Southern University at
http://web.archive.org/web/20031207051746/http://www2.gasou.edu/chemdept/general/molecule/lewis.htm
http://www2.gasou.edu/chemdept/general/molecule/lewis.htm

Lewis Structures by Steven Hardinger at UCLA
http://web.chem.ucla.edu/~harding/lewisdots.html

            A.  Drawing Lewis Structures. 
                        1.  Add all valence electrons and divide by 2.  This gives the number of electron pairs for bonding
                            and nonbonding (lone pairs) purposes. 
                        2.  First connect the atoms with single bonds, then distribute the other pairs as lone pairs. 
                        3.  If some atoms lack an octet try using multiple bonds. 
                        4.  Examples:   H2              F2         O2        N2        CH2O               H2
                                    CH4      C2H6                C2H4                C2H2 
                        5.  Calculate formal charges
                                    FC = Group # - (# unshared electrons + bonds) 
                                    a)         Examples:   CH3+       CH3¯       CH3
∙              H3O+        H2SO3 

See the page on formal charge by Brenda Wojciechowski and Paul Cerpovicz at Georgia Southern University at
http://web.archive.org/web/20040405101827/http://www2.gasou.edu/chemdept/general/molecule/fc.htm
 http://www2.gasou.edu/chemdept/general/molecule/fc.htm

See the page on formal charge by Linda M. Sweeting at Towson State University at
 http://www.towson.edu/~sweeting/enrich/formalch.pdf

Formal Charge by Steven Hardinger at UCLA
http://web.chem.ucla.edu/~harding/tutorials/formalcharge.pdf

See my page on common covalent bonding patterns including the associated formal charges at
 http://www.mpcfaculty.net/ron_rinehart/12A/bondpatt.htm

            B.  Valence Shell Electron Pair Repulsion:  VSEPR 

I have compiled an extensive list of great websites devoted to atomic orbitals and VSEPR at
 http://www.mpcfaculty.net/ron_rinehart/orbitals.htm
Many of these sites require MDL Chime
for viewing [with Netscape™]

See the page on VSEPR by Brenda Wojciechowski and Paul Cerpovicz at Georgia Southern University at
http://web.archive.org/web/20040404034801/http://www2.gasou.edu/chemdept/general/molecule/vsepr.htm
 http://www2.gasou.edu/chemdept/general/molecule/vsepr.htm

1.     Used to predict the shape of a molecule based upon the number of electron pairs about the central atom. 

Total Pairs on
Central Atom

Bonding
Pairs

Nonbonding
Pairs

Shape

Example

Approximate Bond Angle

4

4

0

tetrahedral

CH4

109.5o

4

3

1

trigonal pyramid

NH3

109.5o

4

2

2

angular

H2O

109.5o

3

3

0

trigonal planar

BCl3

120o

3

2

1

angular

NO2

120o

2

2

0

linear

CO2

180o

                        2. Treat multiple bonds as a single electron pair about the central atom. 
                        3.  Hierarchy of repulsion between electron  pairs (from highest to lowest):   
                                    a)  lone-pair - lone-pair 
                                    b)  lone-pair - bonded pair 
                                    c)  bonded pair - bonded pair 
                        4. Electrons in multiple bonds take up more space than those in a single bond.  For this
                                  reason the bond angle between H-C=O in formaldehyde is greater than 120o and  less
                                   than 120o   for H-C-H. 
                        5.  Predict the shape for the following examples:     
                        CH3:¯
        CH2O             CH3+                C2H4             C2H2               H2O2           CO32-

            C. Resonance. 

See the page on Resonance Structures by Brenda Wojciechowski and Paul Cerpovicz
at Georgia Southern University at
http://web.archive.org/web/20040405103053/http://www2.gasou.edu/chemdept/general/molecule/resonan.htm
http://www2.gasou.edu/chemdept/general/molecule/resonan.htm

See the page on resonance structures by Linda M. Sweeting at Towson State University at
 http://www.towson.edu/~sweeting/enrich/aromtheo.pdf

Resonance practice problems by Jim Puckett at Harvard University
 http://www.people.fas.harvard.edu/~puckett/supplement_25.6.02.pdf

Drawing Resonance Structures by Steven Hardinger at UCLA
http://web.chem.ucla.edu/~harding/tutorials/resonance/draw_res_str.html

Most Important Resonance Structure by Steven Hardinger at UCLA
http://web.chem.ucla.edu/~harding/tutorials/resonance/imp_res_str.html

                        1.  Lewis structures show electrons in specific localized regions between two nuclei in a
                                   covalent bond or on a single atom as a lone pair.
                        2.  In certain cases more than one Lewis structure can be drawn for a particular
                                   molecule or polyatomic ion: resonance structures. 
                        3.  Pay particular attention to the meaning of:   

                                                ↔  vs     vs     vs     vs    


      

resonance arrow

reaction arrow

equilibrium arrows

curly arrow

half-curly arrow

Used to join two or more different resonance structures for the same molecule

Indicates a chemical reaction

Indicates a reversible chemical reaction

Indicates origin and movement of a pair of electrons when showing the mechanism of a reaction.
Also useful as a tool when trying to draw additional resonance structures corresponding to a given structure.

Indicates origin and movement of a single electron when showing the mechanism of a reaction.
Also useful as a tool when trying to draw additional resonance structures corresponding to a given structure.

See the Curly Arrows tutorial by Mary Masson at the University of Aberdeen at
http://www.abdn.ac.uk/curly-arrows/
http://www.abdn.ac.uk/curly-arrows/index.html
[we won't really need this for a while, but...]

Curved Arrows tutorial by Steven Hardinger at UCLA
http://web.chem.ucla.edu/~harding/tutorials/curvedarrows/curvedarrows.html

                        4. Resonance hybrids. 
                        5. Resonance represents a breakdown of the Lewis concept since it implies a delocalization of  electrons. 
                        6. Best structures have: 
                                    a)  octets for each atom. 
                                    b)  least formal charge. 
                                    c)  no adjacent like charges. 
                                    d)  charge on proper element (with respect to electronegativity).   
                        7.  Examples: SO2              CO32
¯              C6H6                OPN                CH3CO2¯

            D.  Molecular Dipole Moments.

See Intermolecular Interactions by Roberta Kleinman at Lockhaven University of PA at
http://web.archive.org/web/20031203200658/http://www.lhup.edu/~rkleinma/Chem220/CH1Notes/CH1f.htm
 http://www.lhup.edu/~rkleinma/Chem220/CH1Notes/CH1f.htm

and Polarity and Intermolecular Forces by Roberta Kleinman at Lockhaven University of PA at
http://web.archive.org/web/20020718050954/http://www.lhup.edu/~rkleinma/Chem205/Chapters/CH05toc.htm
http://www.lhup.edu/~rkleinma/Chem205/Chapters/CH05toc.htm

                        1.  Compounds with only nonpolar covalent bonds consist of nonpolar molecules. 
                        2.  Compounds with only polar covalent bonds may consist of either polar or nonpolar
                                    molecules, depending upon the shape of the molecule. 
                                    a)  Asymmetric molecules (with polar covalent bonds) have dipole moments:
                                                 HCl      H2O    CH2
                                    b)  Symmetrical molecules (with or without polar covalent bonds) lack dipole
                                                 moments: 
                                                CO2      CF4      BCl3

For greater appreciation of the importance of dipolar attractions (and other intermolecular attractive forces)
in determining many of the physical properties of compounds, see my page on
Physical Properties and Intermolecular Forces
at
http://www.mpcfaculty.net/ron_rinehart/12A/molforce.htm

III.  Structural Formulas 
            A.  Constitutional Isomers (Structural Isomers). 
                        1.  Compounds which share the same molecular formula but differ in structure, specifically
                                    in their atomic connections. 
                        2.  Example:  C2H6O                                                 

                                                 

                                       Ethyl Alcohol                         Dimethyl Ether
                                      b.p. 78.3 oC                             b.p. -24.9 oC
                                      Liquid at RT                            Gas at RT
                                      Reacts with Na                       No reaction with Na 

                        3.  Structure is extremely important since it determines the chemical and physical                                          properties of a compound.  Other examples: 
                                    a)  Proteins. 
                                    b)  Vitamin C. 

            B.  Writing Structural Formulas. 

See Colby College's Shockwave tutorial "Representing Compounds"
 http://www.colby.edu/chemistry/OChem/DEMOS/Repcmpds.html

See Drawing Organic Molecules by Jim Clark at
http://www.chemguide.co.uk/basicorg/conventions/draw.html#top

The different ways of depicting organic structures are discussed by Bill Robinson of Purdue University at
 http://web.archive.org/web/20030111122114/http://chemed.chem.purdue.edu/organic/topicreview/structures/index.html
http://chemed.chem.purdue.edu/organic/topicreview/structures/index.html 

Guide to drawing organic molecules by Joan Cheng at Harvard University
 http://www.courses.fas.harvard.edu/~chems20/handouts/DrawingOrganicMolecules.pdf

Connectivity: What is attached to what by Roberta W. Kleinman at Lock Haven University of PA
http://web.archive.org/web/20021213073907/www.lhup.edu/~rkleinma/Chem220/home.htm > CH 3
 http://www.lhup.edu/~rkleinma/Chem205/Chapters/CH03/connectivity.htm

SODAR: Sum Of Double Bonds And Rings
a valuable tool to use BEFORE you start drawing structures corresponding to a given formula!
http://www.mpcfaculty.net/ron_rinehart/12A/SODARpag.htm

                        1.  Lewis Structure.             

                        2.  Condensed Structural Formula.   CH3CH2CH2CH2CH3 

                        3.  Carbon Skeleton Formula  (Bond-line Formulas).   

                        4.  Write condensed structural formulas for the following compounds expressed in
                                     carbon  skeleton formulas: 

            a)          b)               c)        d)   

 

Many thanks to Rod Oka of MPC for generously sharing his "Lecture Companion" outline, reproduced here by permission with web references and other goodies added by me.
Structures redrawn using ACD Labs ChemSketch™ and MDL IsisDraw™

updated 9/15/07