Organic Chemistry 1 Lecture Notes .docx - Organic Chemistry...

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Organic Chemistry 1 Lecture (CHE 231) 8/27/2019 1.1 Organic Chemistry o The study of carbon-containing molecules and their reactions. o We will be focusing on the electrons in the compounds Organic compounds contain carbon atoms, while inorganic compounds do not 1.2 Compounds with the same molecular formula but different structures are constitutional isomers Atoms that are most commonly bonded to carbon include N, O, H, and halides (F, Cl, Br, I). Each element generally forms a specific number of bonds with other atoms. 1.3 Covalent bond o A pair of electrons shared between two atoms o Ex: What forces keep the bond at the optimal length? o Attractive forces between two differently charged nuclei o Repulsive forces between the two positively charged nuclei o Repulsive forces between the two negatively charged electrons You can calculate the number of valence electrons by analyzing the e- configuration. Or for group A elements only, you can look at the group number on the periodic table. Group number= # of valence electrons. Lewis-Dot Structures o Draw the individual atoms using dots to represent the valance electrons o Put the atoms together so they share pairs of electrons to fill out their octets.
o Ex: NH 3 + + + o NOTE: The nitrogen has a lone pair of electrons Simple Lewis Structures o Draw the individual atoms using dots to represent the valance electrons. o Put the atoms together so they share pairs of electrons to make complete octets. 1.4 Atoms with an unbalanced or FORMAL charge o Anion: Negatively charged o Cation: Positively Charged Atoms in molecules are typically neutral but can also be ANIONIC or CATIONIC To determine formal charge o Compare the number of valance electrons that it owns to the number of valance electrons that the atoms need to be neutral o EXAMPLE: Consider the formal charge on the atoms in the structure below, and determine if any of the atoms should have a formal charge Carbon needs 4 valence electrons to be neutral (Group IV) Carbon is surrounded by 8 electrons here, but it only owns 4 of them (1 from each of the bonds). Since carbon owns 4 electrons, and needs 4 electrons to be neutral, it does not have a formal charge. Oxygen needs 6 valence electrons to be neutral (Group VI) Oxygen is surrounded by 8 electrons here, but it only owns 7 of them (1 from the bond, plus 3 lone pairs). Since oxygen owns 7 electrons here, and needs 6 electrons to be neutral, it has an extra electron, and therefore has a -1 charge. 1.5
Electronegativity o How strongly an atom attracts shared electrons o EX: o F is the most electronegative atom You can remember the relative electronegativity of the atoms in the same column or row. Three types of Bonds o Covalent Bond: Electrons shared between two atoms, where electronegativity difference is less than 0.5 o Polar Covalent Bond: Electrons shared between the two atoms with electronegativity difference is between 0.5 and 0.7 o Ionic Bond: Electrons are not shared, the two atoms differ in electronegative by more than 1.7, and so the more electronegative atom owns the electrons. 4

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