100318 Symmetry Elements.pdf - i-clicker/REEF question Sigh…let’s try this again What is your major A Chemistry and Chemical Physics B

# 100318 Symmetry Elements.pdf - i-clicker/REEF question...

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i-clicker/REEF question: Sigh…let’s try this again: What is your major ? A Chemistry and Chemical Physics B Pharmaceutical Chemistry C Engineering or Physics D Biology (and related, like biotechnology, etc ….) OR pre-med E Others

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Symmetry Predicting molecular shape is the first step to determining a molecule’s symmetry.

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Symmetry elements Identity operation Unchanged molecule (gives original orientation of molecule) : E Rotation Axis (n-fold) – proper Rotation on an axis 360°/n: C n Mirror Plane Reflection through the plane does not change the object: s (sigma) Inversion Center (Center of Symmetry) Inversion through a single point: i Rotation-reflection Axis (n-fold) – improper Rotation through 360°/n and reflection in a plane perpendicular to rotation axis: S n 360º/5 C 5 E s i S 2 s 360º/2 360º/2
Inversion Center (Center of Symmetry) Inversion through a single point: i i A C B iClicker/REEF: Which of these has an inversion center symmetry element? D) A and C E) All of the above.

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How does this play out in molecules?
Identity operation Unchanged molecule (gives original orientation of molecule) Symbol used: E E = C 1 (360 Rotation) CHFClBr

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Symmetry Elements Rotation axis (n-fold) Symbol used: C n n – order of rotation n = 360°/rotational angle a ( ° ) After rotation through 2 p /n or 360°/n, the object is indistinguishable from its previous orientation C 3 C 5 C 4 All have C 2 axes as well
Symmetry Elements Rotation axis (n-fold) Symbol used: C n n – order of rotation n = 360°/rotational angle a ( ° ) After rotation through 2 p /n or 360°/n, the object is indistinguishable from its previous orientation O H H C 2 N H H H C 3 C 6 ^ slide C 3 C 5 C 4 benzene Any other rotation axes?

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