Questions regarding O-Chem

1. Hydrogen is the antithesis to double and triple bonds, i.e. hydrogen is kryptonite to the double and triple bonds superman.  Since there is only 1 mole of H2 not all of the triple bond can break only one of them.  Therefore the major product should be a.  A chain with seven carbons with a double bond in the middle i.e. choice a.  C. lost a carbon somewhere.  i would go with a.  If there were lots and lots of hydrogen d is possible but unlikely given only 1 mole.

 

2. Aromatic means that there is an even number alternating single and double bonds equal to 4n+2 where n=0,1,2,3,...

http://en.wikipedia.org/wiki/Toluene  All of these compounds are real but they go by aliases (you'll probably have to memorize these.) Counting carbons toluene has only 7 so it won't work.

http://en.wikipedia.org/wiki/Xylene  the "o" is NOT oxygen it actually refers to the placement of the methyl groups.  If two groups are next to each other it is called ortho-whatever or o-whatever.  If there is a carbon between the two side groups then its called para or p-whatever.  And if there are two carbons between side groups then its called meta or m-whatever.  Looking at the picture this clearly has 8 carbons.  C. Will NOT work because dichloro added two chlorine atoms chlorine is NOT carbon therefore dichlorobenzene has only 6 carbons.

D. phenyl means it has 6 carbons butan means means it has 4 carbons for a grand total of 10 carbons i.e. too many.

E. Ethyl means two carbons.  Benzene means 6 with three double bonds i.e. 8 carbons so this one is good.

F. Has 12 carbons.

 

Thus for number 2 I would pick B and E. (Using Wiki is ok as long as its not during a test.)

 

3. How long is the longest chain.  6.  Does it have any double bonds?  Yes.  How many?  Three.  Does this structure have a common name?  Yes.  Benzene.  Thus whatever it is it ends in something benzene.  Which is more important, boring hydro carbon chains or exotic halides.  Correct Halides.  Is either halide more important? No.  So which one comes first alphabetically, chloro or bromo?  Bromo good.  So number starting at bromine.  Now I can either number clock wise or anti clockwise.  Which choice will give us smaller numbers on more pieces.  Good so let's number them clockwise.  How long is that carbon chain?  Good 3.  What do they call a three carbon chain?  Prop.  Good now is it the main chain or a side chain? Is it bigger than six or smaller?  Its smaller.  Good so it is a side chain.  What do side chains end with?  "yl"  Good.  Thus we start numbering and naming.  Put the halides first then the alkane group. And voila! 1-bromo-3-chloro-2-propylbenzene.

 

4.  I think they all will react, but I would check the chapter to make certain.

 

5.  http://en.wikipedia.org/wiki/File:Benzene_Representations.svg

Hybridization is a lumping together of two electron orbitals.  Think of them as the race tracks electrons follow.  S orbitals look like spheres.  P orbitals look like figure 8s or dumbells.  an sp orbital is bulbous on one end and skinky on the other as though a p orbital swallowed the spherical s orbital.  Have you ever had room mates.  There is what is distinctly your stuff.  Then there is the stuff that is distinctly their stuff, but then there's some of the stuff that you have NO idea whose it is.  When dealing with electrons its the same way.  When the two orbitals merge they call them hybridized orbitals because its a combination of s stuff and p stuff and has kind of a unique shape much like a common room in a shared apartment.  Anyway you have only a few choices for hybridized orbitals.  sp3 has four lobes so something like methane

 

   H

    |

H-C-H

    |

   H

 

One central atom and four thingamajigs coming off of it be they hydrogens, lone pair electrons, bromines, big long hair carbon chain or what not there are four things, its doesn't matter what they are all coming off of the central atom.  we call this sp3 hyridization and it is really easy to remember because you can think of it as s1p3 1+3=4 so an sp3 hybrid should have four lobes.  Now its your turn.  How many lobes will a sp2 hybrid have?  If you are paying attention it should have one less than an sp3 so sp2 have a total of not four but 3 lobes.  This is easily double checked by thinking of sp2 as s1p2 where 1+2= you guessed it--3.  So an sp2 hybrid should have three lobes not four.  Carbons in double bonds often have this arrangement.  Consider the following:

 

    H        H

      \      /

#1   C=C  # 2 

      /       \

   Br        CH2CH2CH2CH3

 

 

Carbon #1 has a C, a H, and a Br bonded to it forming three lobes.  Yes one of the carbons is double bonded so there are really two attachments but if you were to circle all of the stuff attached to carbon #1 you would draw three circles.  Thus the hybridization must add up to three lobes sp2.  Similarly Carbon#2 also has three things attached to it.  One double bonded carbon forming one lobe.  One hydrogen atom forming the second lobe.  And one LONG chain of crap I don't care about forming a third lobe.  (If the question had asked about some of the other carbons I might care and carefully draw out the carbons and hydrogens and I would see they all have four things bonded to them making them sp3 like we learned about earlier.)  Notice that when dealing with hybridizations its not the total number of bonds because in carbon that is always 4, but rather the important part is how many different directions are the bonds facing.

 

Last example.

 

Consider the molecule aceylene aka ethyne

 

H-C*C-H

 

Where * is a triple bond between the carbons.  In this case the bonds go only two different directions I would thus say it has two lobes.  Therefore whatever hybridization is going on must add up to 2.  Well, if sp3 adds up to 4.  And sp2 adds up to 3.  Then sp must add up to two.  Sure enough  we think of it as s1p1 1+1=2 Thus if a molecule has only two lobes, i.e. a triple bond it must be sp hybridized.

 

Brief recap.  sp3=4 lobes i.e. all single bonds.  sp2=3 lobes i.e. a double bond.  sp=2 lobes and is usually a triple bond.  NOTE:  This only applies to the carbons.  Hydrogens only have 1 thing attached to them so they will ALWAYS be unhybridized s orbitals.  Hydrogen is like your underwear.  As much stuff as you share and hybridize with your room mates your underwear is probably not among those things.  Hydrogen stays unhybridized carbon's a bit of a swinger with its electrons.

 

Now let's go back to the question. 

 

Benzene is often depicted as something like this:

 

 /  \

| O |

 \  /

 

but you should think of it as something like

                                                                                      

                                                                   

       H 

        |

       C

      /  \\     

H-C     C-H

   ||       |

   C     C-H

  /   \   //

H      C

         |

        H

or    

       H

        |    

       C

      //  \                                                                               

H-C     C-H                                                                                                             

   |       ||                                                              

   C     C-H                                                                           

  /   \\   /                                                         

H      C                                                             

         |

        H    

 

With the double bond bouncing everywhere faster than is possible to measure.  Since each of the carbons has three lobes we could call it sp2 hybridized, but there is a better description.  Delocalized electrons.  I would call it e.  There are no triples, not sp orbitals.  The hydrogens are on the outside not on the ring, there are no chlorines or other halogens thus e is probably the best choice.