organic

• What allows rotation along the carbon-carbon bond in ethane?

  Efficient orbital overlap for the sigma bond
• What does rotation along the C-C bond in ethane result in?

  Changes in energy levels
• What representation is useful for visualizing ethane's conformation?

  Newman projection
• What is the arrangement called when hydrogens in ethane are drawn with dashes and wedges?

  Staggered conformation
• What is the dihedral angle in the staggered conformation of ethane?

  60°
• Why is the staggered conformation of ethane the most stable?

  Electrons in CH bonds are far apart
• What is the energy penalty for transitioning between staggered conformations in ethane?

  12 kJ mol^-1
• What are conformers in the context of ethane?

  Rapidly interconverting isomers
• What do the peaks and troughs in the energy plot of ethane represent?

  Peaks are eclipsed CH bonds, troughs are staggered
• Why is the anti conformation of butane the lowest energy conformation?

  Methyl groups are far apart
• What is the least stable conformation of butane?

  Me-Me eclipsed conformation
• What is the gauche conformation in butane?

  Me groups are 60° apart
• What is the final conformation to consider for butane?

  Me-H eclipsed conformation
• What happens to the energy plot for butane during rotation?

  It cycles through various conformations
• What factors contribute to the anti conformation being the highest in energy for butane?

  Steric and electronic factors
• What is the chair conformation of cyclohexane?

  The most stable conformation of cyclohexane
• How many chair conformations can cyclohexane have?

  Two mirror image conformations
• What types of CH bonds exist in cyclohexane?

  Axial and equatorial
• Why is it important to check the geometry when drawing the chair conformation?

  To ensure bonds are parallel
• What happens during the cyclohexane ring flip?

  Interconversion between two chair conformers
• What is the preferred position for larger substituents on cyclohexane?

  Equatorial position
• What are 1,3-diaxial interactions?

  Unfavorable interactions with axial hydrogens
• How does adding a second substituent to cyclohexane complicate its conformations?

  Possibility of isomers and energy choices
• What is the most stable conformation for trans-1,4-cyclohexanediol?

  Both hydroxyl groups equatorial
• What is the preferred conformation for tert-butyl groups in cyclohexane?

  Equatorial position
• How do you determine the most stable conformation for disubstituted cyclohexanes?

  Draw both chair conformations and compare
• What happens when two cyclohexane rings are fused together?

  They form decalins
• What is the structure of trans-decalin?

  Conformationally locked structure
• Why is cis-decalin easier to draw than trans-decalin?

  Cis-decalin can undergo a chair flip
• What shape does cyclopentane adopt?

  Envelope-type shape
• How does cyclohexene differ from cyclohexane in terms of conformation?

  Hydrogens are pseudo-axial and pseudo-equatorial
• How can we assess the stability of carbocycles compared to linear alkanes?

  By comparing heat of combustion per carbon
• What is the ring strain in small carbocycles?

  Higher due to non-ideal bond angles
• What is the heat of combustion of cyclohexane compared to linear alkanes?

  Similar per CH₂ unit
• What are the key conformations of butane?

  • Anti conformation: Lowest energy, methyl groups far apart
  • Me-Me eclipsed conformation: Least stable
  • Gauche conformation: Methyl groups 60° apart
  • Me-H eclipsed conformation: Higher energy than anti
• What are the key conformations of cyclohexane?

  • Chair conformation: Most stable
  • Two chair conformations: Mirror images
  • Axial and equatorial hydrogens: Different types of CH bonds
• What are the factors affecting the stability of substituted cyclohexanes?

  • Larger groups prefer equatorial position
  • 1,3-diaxial interactions: Unfavorable axial interactions
  • Energy penalties for axial positioning
• What happens when cyclohexane rings are fused?

  • Forms decalins
  • Trans-decalin: Conformationally locked
  • Cis-decalin: Can undergo chair flip
• How does cyclopentane differ from cyclohexane?

  • Cyclopentane is less conformationally rigid
  • Adopts an envelope-type shape
  • Each carbon rapidly takes turns at the 'top'
• What is the significance of ring strain in carbocycles?

  • Higher in 3 and 4 membered rings
  • Cyclohexane is free of ring strain
  • Stability assessed by heat of combustion per carbon