Ethane (C2H6) Hybridization: sp3 Molecular Geometry: Tetrahedral Bond Angles: 109.5 degrees Newman Projections: Staggered conformation: H atoms on the front carbon are positioned between the H atoms on the back carbon, minimizing steric repulsion. Eclipsed conformation: H atoms on the front carbon are directly aligned with the H atoms on the back carbon, leading to maximum steric repulsion. Rotation on C-C bond: 60 degrees Barrier to Rotation: ~2 kcal/mol Ethene (C2H4) Hybridization: sp2 Geometry: Trigonal Planar Bond Angles: 120 degrees Double Bond: π bond formed by the overlap of two p orbitals. Newman Projections: Eclipsed conformation: H atoms on one carbon are directly aligned with the H atoms on the other carbon. Staggered conformation: H atoms on one carbon are positioned between the H atoms on the other carbon. Barrier to Rotation: 66 kcal/mol (cost of one π bond) Unsaturated Hydrocarbons: Contain double bonds (sites of unsaturation) Vulnerable to attack by electrophiles (electron-loving species) Example: Breakdown of polyunsaturated fats Ethane (continued) Eclipsed vs. Staggered conformations: Eclipsed is preferred to staggered despite bond repulsion. In staggered, p orbitals are perpendicular and don't overlap. Going from eclipsed to staggered requires π bond to break. Rotation causes it to change. If H atoms are connected to other molecules/proteins, rotation causes it to change stereochemistry. Eclipsed → Staggered takes little energy, rapidly spinning/changing stereochemistry. 1 barrier to rotation: p-orbitals must be parallel. 1 photon/1 temp needed to rotate. Ethyne (an alkyne/acetylene) - H-C≡C-H Hybridization: sp Linear, no issue rotating Stronger than ethane & ethene (More E put into making the bond) Shorthand for Organic Molecules: Butane Skeletal: Does not show geometry (tetrahedral/109°, sp³ bonds) Ends always have enough H to give C four bonds Connected such that all atoms in the middle have their groups coming out toward you Shows 3-D Newman Projections: Looking down the C-C bond 2 methyl groups opposing each other: anti-conformation (apart from each other) If next to each other: gauche interaction. 2 methyl groups opposing each other: anti-conformation (apart from each other) Gauche interaction Formal Charge Achieve Octet: All carbons will have 4 bonds & 0 lone pairs All nitrogens will have 3 bonds & 1 lone pair All oxygens will have 2 bonds & 2 lone pairs All halogens will have 1 bond & 3 lone pairs Minimum Formal Charge: Formal charge: way to keep track of molecular charges; insight into presence of dipole moments and how they're polarized. Common Molecules: Ibuprofen Acetaminophen Aspirin Formal Charge vs. Oxidation States Formal Charge Example: H - C - H (H = 0, C = 0) Oxidation State Example: H - C - H (H = +1, C = -2) Ox. State ENC = total nuclear charge - core e-s - ½ surrounding e-s Ex. methane: 4 charge - 4 core e-s - ½ surrounding e-s All or nothing give/take sharing; better for ionic (extreme polarization) Formal Charge Any shared e-s are equally divided/share (homolytically split) Ex. C-H bond: C gets ½ e, H gets ½ e Better for nonpolar: realistic sharing (no partial charge)