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

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

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

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

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

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)

1. Stronger bonds are shorter. 2. C-H, N-H, O-H: kcal/mol; 1 ( m, 100 pm) 3. C-C, C-N, C-O: kcal/mol; 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

Table 2-3, p. 35

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

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

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).

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 o C nonpolar CH 3 (CH 2 ) 3 CH o Clarger, more London forces -71 o C more symmetrical -99 o C has polar bond

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 o Cnonpolar CH 3 (CH 2 ) 3 CH 3 36 o Clarger, more London forces

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

Table 2-6a, p. 51

Table 2-6b, p. 51