Home > Organic chemistry > Chemistry 51A Lecture 11 Notes 10/22/09

Chemistry 51A Lecture 11 Notes 10/22/09

Overview

Today is a 51 minute lecture on the confirmations of butane and cyclohexane.

Details

Recall butane is C4H10.  The Newman projection looks down the sigma bond so we can see all of the hydrogens in a line.  Kind of looks like a peace sign.

The zigzag conformation is the anti or the conformer, the one lying in an energy well at the lowest energy.  This is the favorable state of the molecule.

How does the energy of butane change as we rotate the bonds?  The angle between bonds is the dihedral angle.  It is 180 at the anti configuration.

Steric hindrance is when hydrogens get in each other’s way.  The price of steric hindrerance is 0.9 kcal/mol.  This is when two methyl groups are near one another.  The energy of the anti conformer is 0 kcal/mol.  The cost of “gauche” is 0.9 kcal/mol.

We would like an energetic profile for what happens as we rotate the molecule.  Anti and gauche are both stable in energy valleys.  6 kcal/mol is the energy when methyl groups overlap directly, with bond angles of zero.  180 degrees, 60, 0 and 120.

Srreveere steric hindrance with hydrogens eclipsing each other HH  is 0.9 kcal/mol.  4 kcal/mol CH3-H H-H and CH3-H are eclipsed.  This gives us a price chart.

H-H    1 kcal/mol

CH3-CH3    4

CH3-H        1.5

Gauch          0.9

Theta          Energy

0            6

60         0.9     (gauche)

120      4

180      0          (anti -most stable)

240        4

300        6

360        0

The idea of the bond angle versus energy graph is that we react over a energy well to create product.

Cyclopropane is a three membered ring.  C3H6 wants to be tetrahedral at 109.5.  Instead it is at 60 degrees.  It has 27 kcal/mol ring strain means it has  bad C-C-C angles in angle strain.

Make cyclopropane, see eclipsing on H-H bonds.  Torsion strain is eclipsing

Cyclopropane is like a coiled spring.  Burn one mole of cyclopropane at 42 moles.

Cyclohexane has 27 kcal/mole less.  A really powerful propane grill would use cyclopropane.

Cyclobutane is a square.  The angles are 90 degrees.  26 kcal/mol of strain.  Less strain of cyclopropane.  There is some angle strain and torsion strain.  Angle strain is much worse than torsion strain.

Cyclopentane is C5H10.  The bond angles are 108 degrees, virtually the same as tetrahedral 109.5.  It has 6 kcal/mol of ring strain.  The main strain is torsional strain.  There is some hydrogen eclipsing.

Recall cyclohexane is C6H12.  Cyclohexane has two main conformers: the chair conformation and the boat conformation.  The chair conformation is the lower energy state and is cheaper.  The boat form is less favorable and more expensive.

Review

Aging: oxygen, UV light, water, heat

Electronegativity: NOF Cl Kr

Alkane CnH2n+2

Alkene CnH2n

Alkyne CnH2n-2

Most important cyclic molecules: Benzene C6H6/Naphthalene C10H8

Moving formations: column line wedge vee eschelon

When not moving: herring bone and coil

Transversing Terrain: traveling, traveling overwatch, bounding overwatch

breaking bonds takes energy, making bonds releases energy

Loads on average were: – fighting load: 63 lbs – approach march load: 101 lbs – emergency approach march load: 132 lbs

One well-established norm is that a soldier cannot sustain a load greater than one-third of his body weight over time.

Noble gases: He, Ne, Ar, Kr, Xe, Rd

Types of bonding: ionic >1.7, polar covalent between, non polar <0.5

PV = nRT

METT TC mission enemy troops terrain time civilians

SALUTE size activity location unit time equipment

2s 6p 10d 14f

KE electron = E photon – Ionization Energy

Tissue: epithelial, connective, nervous, muscular

Epithelial: simple/stratified/pseudostratified    cuboidal/columnar/squamous

  • single covalent bond – 1 shared pair
  • double covalent bond – 2 shared pairs
  • triple covalent bond – 3 shared pairs

Bond energy: single < double < triple

Bond length: single < double < triple

pKa’s:

Alkanes (50)

CH4/CH3-

Alkene (44)

Alkyne (25

HF +3.2

HCl -7

HBr  -9

HI -10 NH3 38 L

RCOOH (4-5)

HF (3.2)

NH4+ (9.26)

H2O (15.7)

ROH (17)

RSH (11)

H30+  (-1.7)

pKa = – log Ka

Spectroscopy: emission/absorption

A = e l c

IGL: point source, random motion, elastic collisions, high temp, low pressure

6 strong acids:

  • HCl
  • H2SO4
  • HNO3
  • HClO4
  • HBr
  • HI

The stronger the acid, the higher the Ka, the weaker the conjugate base.

hydrogen helium

lithium beryllium boron carbon nitrogen oxygen fluorine neon

sodium magnesium aluminum silicon phosphorus sulfur chlorine argon

potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton

rubidium strontium yttrium zirconium niobium molybdenum technicium ruthenium rhodium palladium silver cadmium indium antimony tin tellurium iodine xenon

cesium barium lutium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon

SWAT – snipers, entry team, inner perimeter/gas people

AOR = area of responsibility

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