CHEM 30B  Dr. R. Rinehart    EXAM 1 Study Guide   2/23/02

 

READ THIS GENERAL STATEMENT CAREFULLY:

            Your mission in this course is to obtain for yourself a useful working knowledge and understanding, at an appropriate level, of some basic organic chemistry and biochemistry, as outlined in the syllabus and subsequently elaborated in class. The resources available to you include: the text, lectures and class handouts -- now posted on this site, laboratory exercises, references in print and on the internet, consultation with the instructor outside of class, tutors on duty in PS-205, or by arrangement, and whatever other legitimate means are necessary. There is no easy path to success. Put the work in. It is particularly important to pay attention to the following sections at the end of each chapter: Concept Summary, Learning Objectives, Key Terms and Concepts, and Key Reactions. In particular, the learning objectives tell you what types of knowledge you will be expected to demonstrate.  You will not be able to demonstrate them unless you understand the principles involved! Similarly, you will find it pointless to memorize key terms without knowing what they mean and how they can be applied.

“Right, sure, yeah, yeah, yeah – just tell us what’s going to be on the test, doc.”

What?  Questions designed to show if you have learned to use these principles and their associated language.

How? Generally by means of objective questions in a variety of formats: fill-ins, short answers, matching, multiple choice, true-false, listing, categorizing, prioritizing, and problem-solving are all possibilities. Naming compounds, drawing structures and/or diagrams, writing (and sometimes balancing) equations, and making rational deductions  are all possibilities.

 

Chapter 11: Alkanes, Cycloalkanes, and Haloalkanes [also Intermolecular Forces & Chime workshops on alkanes]

            covalent bonding : shared pairs of e-
           
C: normally
forms 4 covalent bonds; H and X form 1; O and S form 2; N usually forms 3.
           
hydrocarbons: contain C and H only
           
hybridization: C = 1s22s22px12py12pz0 ,
but this does not explain observed molecular geometry;
                       
we mathematically mix the 2s and 2p orbitals in various ways to get a better description.
            sp3
hybridization 
4 identical sp3 orbitals with tetrahedral geometry,  109o28’ bond angles
           
molecular orbitals =
our picture of how covalent bonds form and their locations
           
sigma (s) bonds:
formed by end-to-end overlap of atomic orbitals like 1s of H and sp3 of C
           
molecular formula:  for alkanes: CnH2n+2 ;  for cycloalkanes
with 1 ring: CnH2n
           
structural formulas : expanded and condensed 
           
skeleton  formula:
  all H’s on C not shown; saves time in writing and looking at complex structures
            structural isomers:
same molecular formula, different pattern of bonding.
                    Results in different compounds with different physical, chemical, and biological properties.
           
physical properties: observed/measured parameters used to characterize compounds.
                       
Include: melting point, boiling point, solubility in water and in other solvents, color, odor,
                                   
density,
electrical conductivity, crystal structure, heat of formation, heat of fusion,
                                    heat of vaporization, refractive index, specific rotation of polarized light,
                                    infrared spectrum, etc……….
                       
Many of these properties are determined by the type and strength of the intermolecular
                                   
attractive forces
between the particles involved. Hence, understanding the types of
                                   
such forces, how they originate, and how they operate is very important.
                        The strongest force available generally determines what happens
in a system.
           
ionic attractions: between oppositely-charged ions. Very strong; strength depends on size of charge,
                     
distance, shielding by solvent, etc.
           
hydrogen bonding: 
special type of interaction between a H bonded to an electronegative atom
                   
such as O or N and the lone pair of electrons on a second electronegative atom. 
                       
Stronger than the next two forces. H-bonding substances can always have dipolar attractions present also,
                        but the reverse statement not true. Important in water, alcohols, proteins, DNA.
           
dipolar attractions: dipoles
form when two covalently-joined atoms have a substantial difference
                       
in electronegativity. A dipole is the electrical analog of a magnet. Opposite poles attract.
                        Generally stronger than dispersion forces.
            London or dispersion forces:
very weak; caused by synchronization of random electron
                         
movements in neighboring molecules via electrical fields. Strongest when there is extensive
                         
surface area of contact. Most significant in nonpolar compounds. Associated with
                         
hydrophobic” substances.
            The three weak forces [H-bonding, dipolar forces, and dispersion forces are collectively referred to as
                         van der Waals forces]
            nomenclature: Nx for alkanes is the basis for Nx of all other classes of compounds.
                       
Based on the Greek words for the number of C’s in the longest “straight” chain;
                         
-ane
is characteristic ending. Prefix cyclo- used for compounds with rings.
                   
Substituents:
use prefixes as alkyl groups, halo groups, with amounts shown by di-, tri-, etc
                    location on chain
specified with numbers [“locants,” use one for each substituent].
           
chemical properties:
the set of characteristic chemical reactions which a substance exhibits.
            characteristic reaction
of alkanes and cycloalkanes:
                (complete) combustion   CxHy + (x + ¼y) O2 à  x CO2 + ½y H2O  (+ heat
and maybe light)
               
[this works for ANY HC]  If sufficient O2 not present, some CO forms (incomplete)
           
natural sources
of alkanes :  petroleum (C5 – C100+) and natural gas (C1 – C4).
                        Supply running low!!!!! 
Prices going up!!!!!!!!! Wars being fought [and planned?]...

  Chapter 12: Alkenes, Alkynes, and Aromatic Hydrocarbons
[also Lab & Chime workshop on unsaturated hydrocarbons]

Collectively these hydrocarbons are called “unsaturated” [with H] because they can be forced to add H2
       
Alkenes
   contain double bonds between C’s; for one C=C, molecular formula = CnH2n
           
sources:  1) petroleum and natural gas   2) thermal “cracking” of alkanes 
                          
3) dehydration of alcohols       4)  treatment of alkyl halides with strong bases
        sp2
hybridization 
3 identical  sp2 orbitals with planar geometry, 120o bond angles;  pz remains
       
pi ( p) bonds:
formed by parallel overlap of the leftover unhybridized pz orbitals
               
C=C
has one s  bond (sp2-sp2) and one p  bond

Characteristic reactions: addition
                        ·        of H2    catalytic hydrogenation: gives alkanes
                        ·        of X2    halogenation: gives vicinal dihalides
                                    [reaction causes orange color of Br2 to disappear – used as test for C=C]

                        ·        of HX hydrohalogenation: gives monohalides
                        ·        of H2O  hydration: gives alcohols
                        ·        of C=C:  leads to polymerization à polyethylene, polypropylene, polystyrene, PVC,
                               
PVA, Saran, Teflon, rubber, …

                        ·        react with purple KMnO4 to give brown/black MnO2 ppt [another test for C=C]       

      Alkynes  contain triple bonds between C’s; for one C≡C, molecular formula = CnH2n-2
           
sp hybridization    
2 identical  sp  orbitals with linear geometry , 180o  bond angles;  {+ py & pz}
           
C≡C
has  one s (sp-sp) and two p bonds (py-py and pz-pz)
           
chemically ~ to alkenes,
but more reactive [acetylene torch]  

       Aromatics
             Aromatic compounds: 
one or more 6-membered rings with alternating single & double bonds;
                       
every ring C is sp2  bond angles 120o 
              
“resonance”
from delocalized electrons more stable than alkenes, react differently
              
sources: coal tar,
synthesis
               uses:
  solvents, starting materials in syntheses; essential components in some biomolecules;
               aromatic hydrocarbons are toxic:
bone marrow depressants, carcinogens, drugs of abuse [glue]

 

Chapter 13: Alcohols, Phenols, Ethers, Thiols [also Lab/workshop on alcohols]

         Alcohols: contain the hydroxyl group attached to C in an alkyl group   ROH
           
Classes: 1o, 2o, 3o  react differently
           
Nx: 
attach suffix –ol to stem name of longest chain containing the –OH, which gets lowest number
           
physical properties: C1-C3 miscible with H2O, C4-C6 soluble in H2O, >C6 insoluble in H2O
                       
relatively high melting and boiling points due to H-bonding
                       
soluble in other alcohols, ethers, acetone, etc.
           
sources: natural: wood à methanol; fermentation à ethanol;  synthesis by hydration of alkenes
           
uses: solvents, antifreeze, moisturizer, flavorings, booze
           
characteristic reactions: 
                        oxidation: complete = combustion;   
                       
incomplete: 1o à aldehydes à carboxylic acids,  2o à ketones,  3o  N.R.
                       
dehydration: acid-catalyzed; at 140oC, intermolecular  2ROH à ROR + H2O
                                                           
at 180oC, intramolecular  RCH2CHOHR’ à RCH=CHR’ + H2O
          
Phenols:  contain the hydroxyl group attached to C in an aromatic ring   ArOH
                       
uses: disinfectants, wood preservatives, embalming agents, antioxidants
          
Ethers:    contain oxygen between two alkyl or aryl groups      ROR’
                   
formed by dehydration of alcohols at 140oC
                   
physical properties: somewhat polar
                   
chemical properties: relatively inert
but the low-mw ones are highly flammable
                   
uses: solvents, general anesthetics, gasoline additives
          
Thiols: contain the thiol (a.k.a. sulfhydryl or mercapto) group attached to C in an alkyl group   RSH
                       
highly odoriferous: skunk essence, onions, garlic, etc.
                       
characteristic reactions: oxidation to form disulfides:  2 RSH  + {O} à RS-SR
                       
reaction with heavy metals:  2 RSH + M2+ à  (RS)2M + 2H+
                       
both rxns important in protein chemistry  

           Multifunctional compounds: have more than one type of functional group, belong to several classes

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© Ronald W. Rinehart, 2002, 2003