Draw a Newman Projection along the C3-C4 for 3,4-dimethylhexane. In the best possible energy conformation, how many gauche interactions are present?

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.