1. Chapter 2: Organic Compounds: A First Look Common Bonding Situations Hydrogen1 bond Carbon4 bonds (neutral and 8 electrons) Reactive Carbon Species

2. Nitrogen3 bonds and one unshared pair of electrons Other relatively stable species

3. Oxygen2 bonds and 2 unshared electron pairs Other relatively stable species hydronium ion

4. Halogens1 bond and 3 unshared electron pairs also 4 unshared pairs and negative charge

5. Phosphorus three bonds and an unshared pair of electrons (like N) also can have more than 8 electrons in its valence shell Sulfurtwo bonds and two unshared electron pairs (like O) also can have more than 8 electrons in its valence shell

6. Bond Strengths and Bond Lengths Bond Dissociation Energy:energy that must be added to break a bond in a homolytic fashion (one electron with each atom)

7. 1. Stronger bonds are shorter. 2. C-H, N-H, O-H: 90-110 kcal/mol; 1 (10 -10 m, 100 pm) 3. C-C, C-N, C-O: 65-80 kcal/mol; 1.5 4. Bonds become weaker and longer down a column 5. C=C is stronger and shorter than C-C (but not two times) C=O is very strong and very common

8. Constitutional Isomers C2H6OC2H6O Constitutional Isomers (Structural Isomers): compounds with the same molecular formula but different arrangements of bonded atoms (different structures, different connectivities) Constitutional isomers have different properties and different chemical reactions. ethanol ethyl alcohol liquid dimethyl ether gas poisonous

9. Hydrocarbons:compounds containing only C and H FormulaNumber of Constitutional Isomers CH 4 1 C2H6C2H6 1 C3H8C3H8 1 C 4 H 10 2 C 5 H 12 3 C 6 H 14 5 C 7 H 16 9 C 10 H 22 75 C 20 H 42 366,319 C 30 H 62 4,111,846,763

10. C 6 H 14 (5 isomers) branched

12. C 5 H 12 3 isomersC 5 H 11 Cl8 isomers

15. C 6 H 14 5 isomersC 6 H 12 many

16. C 6 H 14 is saturated (has the maximum number of H’s for six C’s). General formula=C n H 2n + 2 for a hydrocarbon with maximum H’s (saturated) Remove two H’s to introduce one C=C or one ring. The resulting structure is unsaturated.

17. Degree of Unsaturation (DU) DU = total number of rings plus double bonds for C n H x

18. C 7 H 14 DU = (2)(7) + 2 - 14 2 = 1 So there is one ring or one double bond in C 7 H 14. line structure or Kekule structure condensed structure skeletal structure

20. DU with Other Elements Present halogen monovalent, replaces H one for one, so count as H C 6 H 9 Br= C 6 H 10 DU = 2(6) + 2 –10 2 = 2 oxygendivalent, can insert between two atoms without changing number of H’s, so ignore C5H8OC5H8O= C 5 H 8 DU = 2(5) + 2 – 8 2 = 2

21. nitrogentrivalent, if N is added, must add one more H, so increase maximum H’s by one for each N C 8 H 13 N DU = (2)(8) + 2 + 1 – 13 2 = 3 (triple bond counts as two DUs) or subtract NH from the formula C 8 H 13 N= C 8 H 12 DU = (2)(8) + 2 – 12 2 = 3

22. Physical Properties and Molecular Structure melting point, boiling point, solubility Intermolecular Forces charge interactions larger charges = stronger interaction TypeExample ion-ion very strong ionic bond 188 kcal/mol ion-dipole moderately strong

23. dipole-dipoleweak dipole-induced dipoleweaker instantaneous dipole- induced dipole (London Force) weakest Together these last three are called van der Waals forces (0.5 – 5 kcal/mol).

24. Hydrogen Bonding Hydrogen bonds are stronger than other dipole-dipole attractions because the small size of H allows less distance between the charges (3 – 8 Kcal/mol).

25. Melting Points increase with stronger intermolecular forces increase with more symmetrical shape (molecules pack better into crystal lattice) compoundmelting point NaCl801 o C ionic compound CH 3 CH 2 CH 3 -190 o C nonpolar CH 3 (CH 2 ) 3 CH 3 -130 o Clarger, more London forces -71 o C more symmetrical -99 o C has polar bond

26. Boiling Points increase with stronger intermolecular forces increase with more surface area (more London forces) (rod shaped) increase with hydrogen bonding compoundboiling point NaCl1413 o C ionic compound CH 3 CH 2 CH 3 -42 o Cnonpolar CH 3 (CH 2 ) 3 CH 3 36 o Clarger, more London forces

27. CH 3 (CH 2 ) 3 CH 3 36 o Clarger, more London forces 10 o C less surface area 76 o C more polar 117 o Chydrogen bonding

28. Solubility Like dissolves like. Polar compounds dissolve in polar solvents. Nonpolar compounds dissolve in nonpolar solvents. NaCl dissolves in water. NaCl does not dissolve in CH 3 (CH 2 ) 3 CH 3. CH 3 (CH 2 ) 3 CH 3 and water do not mix (form two layers). CH 3 CH 2 OH mixes with water in all proportions. CH 3 CH 2 CH 2 CH 2 OHis slightly soluble in water (7.4 g/100 mL).

29. Functional Groups Chemical reactions usually occur at or near polar bonds. CH 3 CH 2 CH 2 OHCH 3 CH 2 CH 2 CH 2 OH alkyl group: C’s singly bonded to other C’s and H’s (carbon skeleton or carbon framework) general representation: R- functional group: where chemical reactions occur (double bonds, triple bonds, polar bonds, etc.) R-OH carboxylic acid functional group alcohol functional group