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Organic Chemistry 1 Midterm Key Concepts

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  • Empirical formula (EF) vs Molecular formula (MF)

    EF is the simplest whole-number ratio of atoms in a compound. MF is the actual number of atoms of each element in a molecule.

  • How to determine atomic mass from isotopes

    Calculate the weighted average of isotopes using their relative abundances and atomic masses.

  • Pi bonds formation in molecules

    Pi bonds form from the sideways overlap of p orbitals above and below the bonding axis.

  • Sigma vs Pi bond orbital overlap effectiveness

    Sigma (σ) bonds have more effective orbital overlap than pi (π) bonds due to head-on overlap.

  • Octet rule for boron

    Boron typically has 3 valence electrons and tends to lose 3 electrons to achieve the noble gas configuration of helium.

  • Core and valence electrons for arsenic, antimony, strontium, and beryllium

    Arsenic: 28 core, 5 valence; Antimony: 46 core, 5 valence; Strontium: 36 core, 2 valence; Beryllium: 2 core, 2 valence electrons.

  • Formal charge calculation

    Formal charge = (Valence electrons) - (Nonbonding electrons) - 1/2(Bonding electrons).

  • Skeletal structure representation

    Skeletal structures omit hydrogen atoms bonded to carbons and show carbon atoms as vertices or line ends.

  • Lewis structure and bond angles

    Lewis structures show valence electrons; bond angles depend on hybridization and electron pair repulsions.

  • Condensed structural formula

    A shorthand notation showing the order of atoms and bonding without drawing all bonds explicitly.

  • Degree of unsaturation

    Degree of unsaturation = number of rings + number of double bonds + 2 × number of triple bonds.

  • Constitutional isomers

    Compounds with the same molecular formula but different connectivity of atoms.

  • Resonance structures

    Different Lewis structures representing the same molecule with electron delocalization.

  • Hybridization types

    sp: linear, sp2: trigonal planar, sp3: tetrahedral hybridization of atomic orbitals.

  • Molecular geometry and bond angles

    Bond angles depend on hybridization: sp3 ~109.5°, sp2 ~120°, sp ~180°.

  • Electronegativity and electron density

    Atoms with higher electronegativity have greater electron density and influence reaction sites.

  • Intermolecular forces affecting boiling points

    Hydrogen bonding increases boiling points more than dipole-dipole or London dispersion forces.

  • Determining water solubility

    Water solubility increases with polarity and ability to hydrogen bond.

  • Classification of hydroxyl groups

    Primary (1°), secondary (2°), tertiary (3°) based on the carbon bonded to the hydroxyl group.

  • Removing amines from ether solution

    Use acid-base extraction to protonate amines, making them water soluble and separable from ether.

  • Lewis acid and base identification

    Lewis acid accepts an electron pair; Lewis base donates an electron pair.

  • pH calculation from pKa and ratio of forms

    pH = pKa + log([base]/[acid]); used to find pH when base form concentration is known.

  • Acid strength comparison by pKa

    Lower pKa means stronger acid; citric acid (pKa 3.13) is stronger than lactic acid (pKa 3.86).

  • Why ethoxide cannot deprotonate cyclohexane

    The conjugate acid of ethoxide is weaker than cyclohexane, so the reaction is not favorable.