chem 14c – Chemistry

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Lactone
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an ester contain within a ring
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bond angles
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sp3-109.5
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hybrid orbitals
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sp1
sp2
sp3
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geometry of hybridization
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sp3=tetrahedral
sp2=bent
sp1=linear
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torsional strain
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e- repulsion when an atom passes by another atom/group by rotating
-rotation is allowed as long as it does not significantly decrease orbital overlap.-in newman projection, it is motion of getting the molecules to line up
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steric strain
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strain caused by e- repulsion on an atom/group by another near by atom or group.
-in newman projection, it is when the substituents are line up
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angle strain
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strain resulting from non ideal angles.
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ring strain
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strain from being in a ring, combination of torsional and angle strain.
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functional groups
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group of atoms that determine molecular properties ( chemical, physical, or biological)
-allows use to make predictions about a molecule.
-chemical rxn is influence by e- distribution and molecular structure.
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gauche,stagger, ecilpse.
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gauche-biggest groups 60 degrees next to each other
stagger- evenly spread out
elcipse-overlap
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planar
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-has equal bond angles
-permit p orbital overlap=inc stability
-max p orbital overlap occurrs when p orbitals are parallel(that is when they are planar)=max bond strength and max stability
-conjugations have partial pi bonds (dotted lines in resonance hybrid) that restrict rotation and force planarity
-if there is significant torsional strain, the molecule won’t be planar.
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axial vx equatorial
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axial up and down, equitorial=left/ right
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Resonance:
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when a molecule can be represented in 2 or more valid lewis structure.
– must have a pi orbital, except in rare case where sigma bond break for resonance.
-allows electron delocalization
-e- are delocalize and stablize by resonance
-less e- repulsion the more stable the molecule.
-chemical reaction often produce stable products ( resonance, conjugation, etc)
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Resonance contributor
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one lewis structure that contributes to resonance
-has no physical reality
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resonance hybrid
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a weighted avg of resonance contributor.
– single lewis dont strucutre that takes all of the resonance contributors into account.
-look at this when considering any property (ie: bond length) instead of individual resonance contributor.
-helpful way to locate conjugate atoms
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patterns of resonance:
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1. lone pair pi bond
2. open octet pi bond
3. pi bond lone pair and open octet
4. aromatic ring pi bond circulation ( rotation of pi bond in one ring at a time)
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rules of resonance
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1- most important- full octet
2. max # of covalent bond
3. least number of formal charge.
4. negative charge are best on the most electronegative atom and positive charge are better on the least electronegative ( -)
5. resonance is strong between elements in the same row.
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barrier to rotation:47
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-partial pi bond=higher barrier to rotation=planarity=stability
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heat of formation(ΔHf)
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enthalpy change when a substance is made from an element in their standard state. the smaller the ΔHf means the more stable a molecule is.
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catalytic hydrogenation
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-the adding of a hydrogen, disrupts conjugation ,but doesn’t completely destroy it.
-the lower the entalpy of hydrogenation the more stable the isomer is.
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conjugation
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-the special stability provided by 3 or more adjacent, parallel, overlapping p orbitals
-has partial pi bonds that restrict rotation and force planarity( result of conjugation)
-increase stability
-a planar conformation is required to achieve conjugation
-require atoms to contribute a pi bond (sp and sp2 hybridization)
-unlike resonance, conformation isomers are real structures with distinct lifetimes.
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colors in conjugation
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more conjugated= more color(visible light)
ΔE= HOMO/LUMO gap ( change in energy from ground state to excited state)
-high HOMO/LUMO= uv light
inc pi bond=dec. HOMO/LUMO gap=dec. in energy required to excite an electron
-there is no relationship between the stability of a molecule and its color. stability is determined by the energy of the molecule and color is determine by the difference of energy between 2 molecular orbitals
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partial pi bonds(dotted lines in resonance hybrid)
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-shorter than single bonds, longer than a carbon-carbon double bond
-partial pi bond=higher barrier to rotation=planarity=stability
-two adjacent sp2 atoms have a partial pi bond(or full) due to p orbital overlap
-rotation of sigma bond and torsional strain decrease p orbital overlap destroying partial pi bond and dec. the stability
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coplanar
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pg: 65
when torsional strain destabilization < conjugation stabilization=coplanar(dihedral angle of 0 degrees
-is perpendicular if torsional strain destabilization> conjugation stabilization( ie. 2 methyl group repulsion)
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aromaticity
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the extra stability possessed by a molecule that meets the following criteria:
1. cyclic/ ring structure
2.must have a p orbital
3. pz orbital must overlap and be planar(or close to it)
4. orbital arrangement must result in a lowering of energy: 4n+2
– prevented by torsional strain or steric strain b/c they interfer with p orbtial overlap
-ring strain usually doesn’t interfere with p orbital overlap… so doesn’t prevent aromaticity.
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diradical pg: 69
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a species with two unpaired electron
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hybridization:
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the presence of pi bonds is a result of hybridization not a pi bonds cause hybridization.
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absolute configorations
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relative spatial postion of attachments at the sterocenter. assign r for clockwise and s for counter clockwise.
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chiral
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-non superimposable mirror image
-superimposible mirror image = achiral
-allows optical activity
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priority rule
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lowest priority and in the back for atoms with the lowest atomic number.
lone pairs have no protons or nucleus so its priorit is always lowest.
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diastereomer
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stereoisomer that is not an enantiomer
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enantiomer
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one of a pair of stereoisomer that are non superimposable mirror images
– only physical property of enantiomer is the direction the rotate plane-polarized light
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meso compound
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achiral compound that contains two or more sterocenter
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optically active
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-rotates plane-polarized light
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stereocenter
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carbon atom with four different attachments
-2^n stereocenters at most?
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stereoisomer
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-same molecular formula,but different orientations
a. conformational b.geometrical isomer(14b)
c. optical isomers-two types: diastereomers and enantiomer)
one of a set of isomer of identical constitution(sequence of atomic attachments) but differing in the arrangement of their atoms and non interconvertible by rotation around a single bond
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biological effect
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-when a compound interacts with an enzyme or receptor in the body
-enzyme and receptors are constructed by proteins and have very specific shape and size
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constitutional isomer
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same molecular formula, but different connectivity
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conformational isomers
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different rotation around a single bond
-has a physical reality, unlike resonance
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aldose
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amylopectins
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amylose
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anomeric carbon
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disaccharide
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fisher projection
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furanose
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glycoside
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haworth projection
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hemiacetal
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hexose
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ketose
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pentose
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polysaccharide
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pyranose
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saccharide
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tetrose
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triose
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α and β and D configuration
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-refers to the stereochemistry at the anomeric carbon
d= means the carbohydrate has the most common natural configuration
-alpha is easier to break down than beta
α if when the CH2OH and OR groups are trans in the α anomer.
-β when CH2oh and anomeric group are cis in the β anomer

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