1. Hybridized Atomic Orbitals
CH4 (methane): C needs 4 atomic orbitals for C-H bonds
Does excitation below give geometry consistent with that observed for CH4?
Expected Geometry:
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Klein, Organic Chemistry 2e

2. Hybridized Atomic Orbitals
CH4 (methane): C needs 4 atomic orbitals for C-H bonds
Does excitation below give geometry consistent with that observed for CH4?
Expected Geometry:
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Klein, Organic Chemistry 2e

3. Hybridized Atomic Orbitals
Methane looks like this:
4 equal C-H bond lengths
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Klein, Organic Chemistry 2e

4. Hybridized Atomic Orbitals
C atomic orbitals hybridize to form 4 symmetrical equal-energy atomic orbitals
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Klein, Organic Chemistry 2e

5. Hybridized Atomic Orbitals
Note: the shape of an sp3 orbital.
It’s 3 parts p orbital, 1 part s orbital
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Klein, Organic Chemistry 2e

6. Hybridized Atomic Orbitals
To make CH4
the 1s atomic orbital of each H atoms will overlap with the four sp3 hybrid atomic orbitals of C (4 sigma (σ) bonds are made) σ σ σ σ
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Klein, Organic Chemistry 2e

7. Hybridized Atomic Orbitals
Draw a picture that shows the necessary atomic orbitals and their overlap to form ethane (C2H6). (Don’t worry about geometry for now)
Draw a picture that shows the necessary atomic orbitals and their overlap to form H2O. (Don’t worry about geometry for now)
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Klein, Organic Chemistry 2e

8. Hybridized Atomic Orbitals
Consider ethene (ethylene).
Each carbon in ethene must bond to 3 other atoms, so only 3 hybridized atomic orbitals are needed
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Klein, Organic Chemistry 2e

9. Hybridized Atomic Orbitals
An sp2 hybridized carbon will have three equal-energy sp2 orbitals and one unhybridized p orbital
Which is lower in energy, the sp2 or the p? Why?
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Klein, Organic Chemistry 2e

10. Hybridized Atomic Orbitals
The sp2 atomic orbitals overlap to form sigma (σ) bonds
Sigma bonds provide maximum HEAD-ON overlap
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Klein, Organic Chemistry 2e

11. Hybridized Atomic Orbitals
The unhybridized p orbitals in ethene form pi (π) bonds, SIDE-BY-SIDE overlap
p–p π (“pee pee pie”)
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Klein, Organic Chemistry 2e

12. Hybridized Atomic Orbitals
Why is sp2 hybridization not appropriate for methane (CH4)?
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Klein, Organic Chemistry 2e

13. Hybridized Atomic Orbitals
Consider ethyne (acetylene).
Each carbon in ethyne is bonded to 2 other atoms, only 2 hybridized atomic orbitals are needed
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Klein, Organic Chemistry 2e

14. Hybridized Atomic Orbitals
The sp atomic orbitals overlap HEAD-ON to form sigma (σ) bonds while the unhybridized p orbitals overlap SIDE-BY-SIDE to form pi bonds
Practice with SkillBuilder 1.7
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Klein, Organic Chemistry 2e

15. Hybridized Atomic Orbitals
Which should be stronger, a pi bond or a sigma bond? WHY?
Pi bonds involve sideways overlap
sigma bonds involve head on (i.e. axial overlap)
Axial overlap is stronger than sideways overlap
Which should be longer, an sp3 – sp3 sigma bond overlap or an sp – sp sigma bond overlap?
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Klein, Organic Chemistry 2e

16. Hybridized Atomic Orbitals
Explain the different strengths and lengths below.
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Klein, Organic Chemistry 2e

17. Molecular Geometry
Valence shell electron pair repulsion (VSEPR theory)
Valence electrons (bonded and lone pairs) repel each other
To determine molecular geometry…
Determine the Steric number
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Klein, Organic Chemistry 2e

18. Molecular Geometry
Valence shell electron pair repulsion (VSEPR theory)
Valence electrons (bonded and lone pairs) repel each other
To determine molecular geometry…
Predict the hybridization of the central atom
If the Steric number is 4, then it is sp3
If the Steric number is 3, then it is sp2
If the Steric number is 2, then it is sp
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Klein, Organic Chemistry 2e

19. sp3 Geometry
For any sp3 hybridized atom, the 4 valence electron pairs will form a tetrahedral electron group geometry
Methane has 4 equal bonds, so the bond angles are equal
How does the lone pair of ammonia affect its geometry?
The bond angels in oxygen are even smaller, why?
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Klein, Organic Chemistry 2e

20. sp3 Geometry
The molecular geometry is different from the electron group geometry. HOW?
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Klein, Organic Chemistry 2e

21. sp2 Geometry Calculate the Steric number for BF3
Electron pairs that are located in sp2 hybridized orbitals will form a trigonal planar electron group geometry
What will be the molecular geometry?
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Klein, Organic Chemistry 2e

22. sp2 Geometry How many electrons are in Boron’s unhybridized p orbital?
Does this geometry follow VSEPR theory?
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Klein, Organic Chemistry 2e

23. sp2 Geometry
Analyze the steric number, hybridization, electron group geometry and molecular geometry for this imine?
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Klein, Organic Chemistry 2e

24. 1.10 sp Geometry
Analyze the Steric number, the hybridization, the electron group geometry, and the molecular geometry for the following molecules
Can you draw the Lewis structures?
BeH2
CO2
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Klein, Organic Chemistry 2e

25. 1.10 Geometry Summary Klein, Organic Chemistry 2e
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Klein, Organic Chemistry 2e

26. Molecular Polarity Electronegativity Differences cause induction
Induction (shifting of electrons WITHIN a molecular orbitals) creates a dipole moment.
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Klein, Organic Chemistry 2e

27. Molecular Polarity Dipole moment =
[amount of partial charge] x (distance charges are separated]
Dipole moment (μ) is reported in units of Debye (D)
1 debye = esu ∙ cm
esu (electrostatic unit)
1 e- charge = 4.80 x esu
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Klein, Organic Chemistry 2e

28. Molecular Polarity Consider the dipole for CH3Cl
Dipole moment (μ) = charge (e) x distance (d)
While we will not calculate dipole moment values, we should be able to draw a vector showing the direction of a molecular dipole
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29. Molecular Polarity What atom will be attacked by OH–
Draw 2 curved arrows to show movement of electrons to demonstrate the “attack”
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30. Molecular Polarity
For molecules with multiple polar bonds, the dipole moment is the vector sum of all dipoles
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Klein, Organic Chemistry 2e

31. Molecular Polarity
1) Determine correct molecular geometry BEFORE analyzing polarity.
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Klein, Organic Chemistry 2e

32. Molecular Polarity
Electrostatic potential maps are often used to give a visual depiction of polarity
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Klein, Organic Chemistry 2e

33. Intermolecular Forces
Many physical properties such as:
Solubility
Boiling Point
Density
State of matter
Melting Point
are affected by the attractions BETWEEN molecules
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Klein, Organic Chemistry 2e

34. Intermolecular Forces
Neutral molecules (polar and nonpolar) are attracted to one another through…
Dipole-dipole interactions
Hydrogen bonding
Dispersion forces (a.k.a. London forces or fleeting dipole-dipole forces)
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Klein, Organic Chemistry 2e

35. Dipole-Dipole
Dipole-dipole forces result when polar molecules line up their opposite charges.
Acetone (from e.g., Lowes) has permanent dipole.
Recall:
The dipole-dipole attraction affets b.p. and and m.p.
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Klein, Organic Chemistry 2e

36. Dipole-Dipole
Why do isobutylene and acetone have such different MP and BPs?
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Klein, Organic Chemistry 2e

37. Hydrogen Bonding Hydrogen bonds are strong dipole-dipole attraction
Hydrogen bonds have relatively large δ+ and δ–
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Klein, Organic Chemistry 2e

38. Hydrogen Bonding
A (H)ydrogen attached to a highly electronegative atom (O, N, F) will have a large δ+ charge
The H (δ+) can attract large δ– (such as lone pair e–) on other molecules
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Klein, Organic Chemistry 2e

39. Hydrogen Bonding H-bonds are about 20 X weaker than covalent bonds
Compounds with H atoms that are capable of forming H-bonds are called protic
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Klein, Organic Chemistry 2e

40. Hydrogen Bonding
Which of the following solvents are protic (have an H capable of H-bonding)
Acetic acid
Diethyl ether
Methylene chloride
Dimethyl sulfoxide
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Klein, Organic Chemistry 2e

41. Hydrogen Bonding
Explain why the following isomers have different boiling points
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Klein, Organic Chemistry 2e

42. Hydrogen Bonding H-bonds help cause DNA to form a double helix
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Klein, Organic Chemistry 2e

43. London Dispersion Forces
Nonpolar molecules (dipole = 0 D) will they attract one another
HOW?
Since nonpolar molecules normally have their e– spread out evenly around the nuclei (+) completely balancing the charge
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Klein, Organic Chemistry 2e

44. London Dispersion Forces
However, electrons are in constant random motion within their Molecular Orbitals
This causes a temporary electron distribution that is NOT evenly balanced with the positive charge of the nuclei
This induces a temporary dipole in a neighboring molecule
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Klein, Organic Chemistry 2e

45. London Dispersion Forces
London Dispersion Forces are short-lived and are generally weak
Enough of them can add up to a lot
Recall last part of video
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Klein, Organic Chemistry 2e

46. London Dispersion Forces
London dispersion forces are strong enough to support the weight of the Gecko
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Klein, Organic Chemistry 2e

47. London Dispersion Forces
Explain why molecules with more mass generally have higher boiling points
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Klein, Organic Chemistry 2e

48. London Dispersion Forces
Explain why more highly branched molecules generally have lower boiling points
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Klein, Organic Chemistry 2e

49. Solubility We use the principle, like-dissolves-like
Polar compounds generally mix well with other polar compounds
If the compounds mixing are all capable of H-bonding and/or strong dipole-dipole, then there is no reason why they shouldn’t mix
Nonpolar compounds generally mix well with other nonpolar compounds
If none of the compounds are capable of forming strong attractions, then no strong attractions would have to be broken to allow them to mix
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Klein, Organic Chemistry 2e

50. Solubility
We know it is difficult to get a polar compound (like water) to mix with a nonpolar compound (like oil)
We can’t use just water to wash oil off our dirty cloths
To remove nonpolar oils, grease, and dirt, we need soap
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Klein, Organic Chemistry 2e

51. Solubility
Soap molecules organize into micelles in water, which form a nonpolar interior to carry away dirt.
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Klein, Organic Chemistry 2e