Organic Chemistry Chapter 6 and 7 – Flashcards
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alkyl halide
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halogen atom bonded to an sp3 hybridized carbon atom that is tetrahedral
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primary alkyl halide
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One carbon attached
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secondary alkyl halide
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2 carbons
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tertiary alkyl halide
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3 carbons
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aryl halides
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halogen bonded to an aromatic ring
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Nucleophilic substitution reactions
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a nucleophile displaces a leaving group in the molecule that undergoes the substitution
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electrophile
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electron loving (needs more electrons) Gets rid of the positive charge
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leaving group
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always a species that takes a pair of electrons with it when it departs
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nucleophile
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always a lewis base, may be negatively charged or neutral (wants to get rid of electrons)
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always a lewis base
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nucleophile
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any negative ion or uncharged molecule with an unshared electron pair is a
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potential nucleophile
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a good leaving group is a substituent that can leave as
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a relatively stable, weakly basic molecule or ion
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bimolecular
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two species are involved in the step whose rate is being measured
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Sn2 reaction means
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substitution, nucleophilic, bimolecular
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Sn2 reaction undergoes
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inversion (its tetrahedral bonding configuration is turned inside out)
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transition state
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a state on a potential energy diagram corresponding to an energy maximum
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reaction coordinate
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indicates the process of the reaction, in terms of the conversion of reactants to products
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free-energy diagram
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plot free energy of the reacting particulate (y-axis) against the reaction coordinate (x-axis)
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free energy of activation
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difference in energy between the reactants and the transition state
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free energy change for the reaction
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the difference in energy between the reactants and the products
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the top of the energy hill corresponds to
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the transition state
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uphill on potential energy diagram is
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endergonic
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downhill on potential energy diagram
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exergonic
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as you go down the periodic table the atoms get larger making longer bonds that
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lower the energy
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as you go down the periodic table the atoms get
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larger
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physical properties of organic halidees
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low solubility in water soluble in nonpolar sovlents
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Mechanism of Sn2
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1 step transition state inversion attack from the back
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nucleophiles approaches from what side in sn2 reactions
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back side, away from the LG
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carbocations are
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trigonal planar
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carbocations have
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2 empty p orbitals
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Sn1and optical active compounds
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optically active substrate transformed into racemic products
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Solvolysis
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the solvent act as the nucleophile in a substitution reaction
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hyper conjugation
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electron delocalization from a filled orbital to an adjacent unfilled orbital
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hyper conjugation does what to carbocations
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stabilized
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Sn1 mechanism
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1. nucleophilic attack 2. solvent used 3. charges balances (possible use solvent again)
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stability of carbocations
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increase the number of C attached to the center c, makes the carbocation more stable
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carbon compounds are never
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the leaving group
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steric hinderance
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an affect on the relative reaction rates caused by the space-filling properties of those parts of a molecule attached at or near the reacting site hinders a reaction
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steric hinderance is due to
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space filling properties
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negatively charged nucleophiles are more reactive than their
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conjugate acids
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the lower the pKa
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the stronger the acid, the weaker the base
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The higher the pKa
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the weaker the acid, the stronger the base
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nucleophilicity parallels basicity when comparing nucleophiles with the same nucleophilic atom
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RO- > HO >> RCO2- > ROH > H2O
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nucleophilicity is measured by
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relative rates of reaction
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steric hinderance blocks
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where the nucleophile can come and attack the carbocation
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molecules that great the slowest will not likely react via an Sn2 pathway, though what other pathway might such molecules proceed?
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they are too bulky to travel via Sn2 pathway (steric hinderance) so they are able to go down an Sn1 pathway
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the more - charged nucleophile the
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faster the reaction
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nucleophilicity parallels basicity when comparing nucleophiles with the same electrophilic atom (example)
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RO- > HO >> RCO2- > ROH > H2O
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nucleophilicity
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how well the nucleophile performs
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lewis acid
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accepts
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4 factors that affect the rates of Sn1 and Sn2 reactions
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1. the structure of the substrate 2. the concentration and reactivity of the nucleophile (for bimolecular reactions only) 3. The effect of the solvent 4. The nature of the leaving group
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solvolysis
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nucleophile is a molecule of the solvent (sn1)
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Sn2 order of reactivity
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methyl > primary > secondary >> tertiary
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steric hinderance
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spatial arrangements of the atoms or groups at or near the reacting site of a molecule hinders or retards a reaction
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hammond-leffler postulate
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the structure of a transition state resembles the stable species that is nearest it in free energy
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Since the nucleophile does not participate in the rate-determining step of an Sn1 reaction
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the rates of Sn1 reactions are unaffected by concentration or identity of nucleophile
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Relative nucleophile strength
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1. a negatively charged nucleophile is always a more reactive nucleophile than its conjugate acid 2. In a group of nucleophiles in which the nucleophilic atom is the same, nuclophilictges parallels basicities
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Which one is a better nucleophile HO- or ROH
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HO- (negatively charged)
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protic solvent
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has a hydrogen atom attached to an atom of strong electronegative element
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aprotic solvent
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solvents whose molecules do not have a hydrogen atom that is attached to an atom of strongly electronegative element
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rates of Sn2 reactions generally are vastly increased when they are carried out
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in polar aprotic solvents
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what are good leaving groups
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weak bases
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what is a protic solvent
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a solvent with an O-H or a N-H bond which can serve as a source of protons (H+)
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3 types of solvents common come upon
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non-polar, polar aprotic, and polar protic.
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rates of Sn2 reactions are significantly increased in
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polar aprotic solvents
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rates of Sn1 reactions are significantly increased in
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polar protic solvents
