CHEM-C 341 Chapter 2: C341 Ch. 2 Notes (Jan. 18)

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C341 Chapter 2 Notes- Structure and Reactivity; Acids and Bases, Polar and Nonpolar Molecules 1-18-17
Section 2.1- Kinetics and Thermodynamics of Simple Chemical Processes
Simple reactions can be described as equilibria between different species
2 themes (often but not necessarily related):
o Chemical thermodynamics- focuses on changes in energy that occurs when reactions proceed;
controls extent to which reaction goes to completion
o Chemical kinetics- focuses on velocity/rate at which reactant and product concentrations change;
describes speed at which reaction goes to completion
Reaction that gives most stable products is under thermodynamic control
o Outoe of reatio is differee i eergy of produts ad reatats
Reaction that gives products most quickly is under kinetic control
o Products may not be most stable thermodynamically
Equilibria governed by thermodynamics of chemical change
o All reactions reversible to some degree
o State of equilibrium- concentrations of reactants/products stop changing
o Goes to completion when equilibrium lies vastly (usually > 99%) on side of product(s); considered
irreversible
o Equilibrium constant   
 for reaction     , where all concentrations in 
, but
itself has no unit
Large - product favored, large driving force
Small - reactant favored, small driving force
o Gibbs standard free energy change  ( 
)- at equilibrium,    ,
where  standard enthalpy of reaction ( 
),  standard entropy of reaction ( 
,  

   
,   temperature (kelvin)
 - spontaneous reaction, free energy released (equates to large )
 - nonspontaneous reaction, free energy consumed (equates to small )
o  can be estimated well by calculating  

 - thermodynamically favored (exothermic), products have less energy than reactants
 - thermodynamically unfavored (endothermic), products have more energy than
reactants
o  found by looking up or knowing values for specific molecules
 - decrease in disorder of system; energy content of system distributed over smaller
number of particles
 - increase in disorder of system; energy in system distributed over larger number of
particles (ie. 1-pentene ethane + propene)
Section 2.2- Usig Cured Eletro-Pushig Arros to Desrie Cheial Reatios
Reactions follow logical mechanisms- do’t have to memorize every reactive possibility
Curved arrows () show how reactants convert to products by depicting  movement from lone pair
or oalet od to target ato that attrats  with electronegativity or  deficiency
Reaction mechanism uses arrows to show  movement that describes reaction
 move toward more electronegative atom; more readily accepts  pairs to become negatively
charged
Head of first arrow points to tail of second, so both arrows form sequence of movement
General cases:
o Dissociation of polar covalent bond into ions:     (curved arrow goes from  bond to
more electronegative atom to complete octet)
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Ex.    
Ex.    
o Formation of covalent bond from ions:   (curved arrow goes from a lone pair on anion
to anion)
Ex.   
Arrow goes from lone pair on  to atom
Acid-base reaction between hydrogen ion and hydroxide
Ex.  
Arrow goes from 1 of 4 lone pairs on  to to form bond
o Single replacement reactions (simultaneous making and breaking of bonds):    ,
where in  is and in  is 
Ex.     
Curved arrow from lone pair on  to in , curved arrow from  bond to  atom
 bond broken, new  bond made from lone pair
Chloride ion released with additional lone pair (complete octet)
 acts (familiarly) as a base, attacking and removing proton from acid
Ex.      
Curved arrow from lone pair on  to in , curved arrow from  bond in  to
 atom
 bond broken, new  bond made
 pair on  attacks non-hydrogen atom (a carbon in polar bond with )
Carbon in  is electrophilic
o Full or partial positive charge (equivalent of Lewis acid- electron acceptor)
o Has empty orbitals that are attracted to electron-rich site
o Accepts  in reaction to bond in order to bond to nucleophile
Oxygen in  is nucleophilic
o Full or partial negative charge (equivalent of Lewis base- electron donor)
o Basic atom that attacks non-hydrogen atom
o Any atom with lone pairs or at least 1 bond
o Gives  to electrophile to form bond during reaction
o Reactions involving double or triple bonds:
  , where in    is and in    is  (polar bond)
Curved arrow from lone pair on  to in   , curved arrow from bond in    to
atom
Movement of lone pair toward double bond produces single bond between and and
changes double bond to single
Addition of  changes from  to fully negative
Ex.     
o Curved arrow from lone pair on  in  to , curved arrow from bond to atom
in  
o Forms compound with all single bonds
o  acts as nucleophile and adds  to electrophilic to form bond
   
Curved arrow from bond in    to cation, forming new bond and reducing double
bond to single
Ex.    
o Curved arrow from bond in ethylene to proton; forms compound with carbocation
and all single bonds
o Known as protonation of a double bond
o Proton acts as electrophile, attacking  pair in double bond
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o Technique allows keeping track of all s
o Automatically gives correct Lewis structures of product(s)
Section 2.3- Acids and Bases
According to Brønsted-Lowry:
o Acid = proton donor; in water, donates to form
o Base = proton acceptor; in water, removes to form 
Ex.     
o Curved arrow from lone pair on to in  to form bond, curved arrow from  bond to 
atom to break bond
o  = base,  = acid, = conjugate acid of ,  = conjugate base of 
Ex.  
 
o Curved arrow from lone pair on to in  to form bond, curved arrow from bond in  to
in  to break bond and result in 
o  = base,  = acid, 
= conjugate acid,  = conjugate base
Acid and base strengths measured by equilibrium constant
o    
o For general acid , dissociation expressed as equilibrium:
    

 does not include water (pure liquid)
o Similar to , can define   and  -  at which acid is 50% dissociated
High 
Weak acid
Strong base
Low 
Strong acid
Weak base
Strong acid having low  makes sense- it will have large , meaning reaction strongly
product (conjugate base) favored; strong acids considered to dissociate completely into
and conjugate base
Weak acid having high  makes sense- will have small , meaning reaction strongly reactant
(acid) favored; weak acids considered to only dissociate partially or not much at all
o  is conjugate base of - formed from acid; species remaining after acid deprotonates in
reaction
o is conjugate acid of - formed from base; result of protonating base in reaction
Can estimate relative acid and base strengths from molecular structures
o More stable conjugate base () = lower strength as a base (less likely to re-protonate) = more
strength as an acid ()
o Electronegativity of
Acidic proton being attached to more electronegative atom = more polar bond = more acidic
proton
As electronegativity increases, increasing bond polarity means more easily donated, because
can maintain negative formal charge more easily (it can remain stable)
Ex.     
o Size of
Acidic proton being attached to larger atom = poor overlap between larger outer orbital shell
and  hydrogen orbital = weaker  bond = more easily broken up/dissociated
Larger valence shell allows  to spread over larger surface area, reducing electron-electron
repulsion in resulting anion  (compensates for negative charge more easily, becomes more
stable conjugate base)
Ex.      
o Resonance in 
Allows delocalization of  (charge) over several atoms
Effect increased by presence of more electronegative atoms in 
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