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Bond angles
- No of ?things? around central atom (ELECTRON DOMAINS), Geometry, bond angle, hybridization
- 2, linear, 180, sp
- 3, TRIgonal planar, 120, sp2
- 4, TETRAhedral, 109.5, sp3
- Have to count lone pairs, as well as elements bonded when looking at angles
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Hybridization
- Change atoms undergo to form bonds
- Sp, sp2, sp3
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Condensed formula vs structural formula
- One that is written on 1 line of type
- NH3, versus the LEWIS structure (structural formula) drawn out w lone pairs on N
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Line-bond formula
- Line points each represent carbon atom
- No HYDROGEN drawn on carbon
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Sigma and pi bonds in a structure
- Single covalent bond = one sigma
- Double bonds = one sigma and ONE pi
- Triple bonds = one sigma and TWO pi
- ie CH4: each single bond of C-H = 1 sigma, so 4 total sigma and no pi
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Exceptions to hybridization
- Happens mostly in aromatic rings and AMIDES
- Lone pairs that are next door to another element bonded to a double bond will actually donate lone pairs to the bond connected to the double bond (resonance)
- Changes the sp3 to sp2 hybridization in an amide (NH2 bonded to C double bond O) and N would now be + charged with sp2, with oxygen being neg charged with 3 sets of lone pairs?results in double bond between N and C instead of the CO originally
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Resonance structures
- Pi electrons that move from atom to another in some molecules
- Similar to moving doors on a hinge
- The various options are the resonance CONTRIBUTORS
- The resonance hybrid is the mix of going between the various versions
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Resonance structure rules
- Only ELECTRONS move
- You CAN move electrons towards atom that does NOT have full octet
- If atom has FULL OCTET, you CAN move into ONLY if you u push electrons out the opposite side (e in and e out)
- DO NOT move or break sigma bonds, ONLY PI bonds move
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Which is the greater resonance contributor when multiple exist
- It?s always the most STABLE, based on:
- 1. The one with the FULL OCTET on EVERY atom
- 2. The one with the SMALLEST CHARGES
- 3. The one with NEGATIVE CHARGES on most ELECTRONEG atoms
- 4. Most POSITIVE CHARGES on the LEAST ELECTRONEGATIVE atoms
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Radicals
Molecules with unpaired electrons, drawn as single dots
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Newman projection
- Looks at the perspective of looking through both carbons as if they were directly in front and back of each other
- Most stable: staggered option
- Least stable: eclipsed (other elements attached to carbon appear almost directly in front and behind each other
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Cycloalkanes:
- Cyclic alkanes
- Cyclopropane is smallest
- Have 4 single bonds around them, the ideal bond angle being 109.4 (tetrahedral)
- Since the propane ring has 60degree angles between, it?s constrained
- This ring is termed ANGLE STRAINED, since it wants to be 109.4 (C with 4 bonds)
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Most stable ring
- CycloHEXANE
- Bond angles between a hexane ring is 120
- The bond spacing of these C are allowed to be 109.5 or as close as possible, in the CHAIR conformation
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Axial vs Equitorial
- When looking at a CHAIR conformation:
- Hydrogens going up or down straight: AXIAL
- Hydrogens jetting out at ANGLES: Equitorial (more stable)
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Drawing Axials first, then equitorials
- First, look at each carbon and depending if it?s going more upward or downward, draw either axial up or down
- Second, as which direction axial is pointing, and equatorial will go opposite direction.
- IE: If the Axial is UP, EQUITORIAL needs to go Down, but not straight, at an angle downwards
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Equitorial spacing
- Because they are separated by 1,3 carbons, they are favored vs the axial
- If there are other appendages besides Hydrogen on these rings, the most stable form will be the one with appendages that are placed in equatorial positions vs up and down axial, as well as having the largest substituent in the Equitorial position
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Trans vs Cis cyclohexanes:
- If you have 2 substituents both going same direction: CIS to each other
- If the 2 substituents are going up and down: TRANS to each other
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