Cyclohexane+Conformations++If+all+6+carbon+atom s+of+cyc lohe xa ne+a re+in+the +sam e +plan e+the n+the +bon d+a ng les+ar e+forced+to+be+120°+and+the+C<H+bonds+on+adjacent+C+atoms+are+eclipsed.+In+order+to+avoid+the+angle+(120+vs+10 9 )+a n d +torsional+strain+(eclip s e d +b o n d s )+imposed+b y +th e +p la n a r +co n f o rmation,+the +r in g +p u c k e rs +in to +a +“ c h ai r” +conformation.+++ ++++++++Top+Vie w+Planar++++++++++++++Side+View++Planar+++++++++++++++++++++++++++++++++++++Side+View+Chair++++++++++++++++++++++++++++++++++++++++++When+it+adopts+the+chair+con fo r mation,+the +C<H+bonds+adopt+one+of++tw o +distinct+orie n ta ti o n s,+a x ia l+or+equatorial.++Axial+H’s+point+straight +u p +or +stra ig h t+d own.++Equato ria l+H ’s+ point+away+from+the+ring,+but+are+also+angled+up+or+down.+Each+C+atom+has+one+axial+and+one+equatorial+H,+++“pointing”+in+oppo site+directions.+++++The+cylcohexane+ring+is+not+locked+into+one+chair+conformation,+but+can+flip+back+and+forth+between+2+chair+conformations+of+equal+energy.++When+th e +c y cl o h e x an e +c h a ir +u n d e rg o e s +th is +co nformatio n a l+change+it’s+called+a+ring+flip.++The+ring+flip+is+the+result+of+bond +r o ta t io n s +in +th e +r in g ,+a n d +ca n +b e+pictured+by+imagining+the+chair+forming+a+“boat”+and+then+back+to+a+chair.+++++ + + + + +++++++++Ring+Flip ++++As+the+ring+flips,++the+C<C+bonds+rotate,+and+the+C<H+bonds+change+orientations.+Axial+C<H+bonds+in+one+chair+conformation,+are+equatorial+C<H+bonds+in+the+other+cha i r+c o n fo r mation.++++HHHHHHHHHHHH*#*#*#HHHHHHHHHHHHHHHHHHHHHHHHSubstituted+Cyclohexane+Conformations++When+a+cyclohexane+ring+has+one+or+more+substituents,+the+two+chair+conformations+are+often+no+longer+of+equ al+en e rgy ,+du e+to +1,3 <diaxial+interactions+between+atoms+in+axial+positions+on+the+same+side+(top+side+or+bottom+side)+of+the+ring.++++Top+View+Planar+++++++++++++++Side+View+Planar++++++++++++++++Side+View+1st+Chair+++++++++++++++++++++++++Sid e +V ie w+2nd+Chair+++Converting+Multi<substituted+Planar+structures+into+Chair+Conformations.++Example:+trans<1<isopro p y l<3<methylcyclohexane++++1) Convert+planar+(flat)+structure+to+chair.+a. Draw+axial+bonds:+Start+at+the+“head”+carbon+and+draw+the+axial+bond+pointing+up,+then+alternate+around +the+ring+do w n+an d+up .++b. Draw+equatorial+bonds:+Start+at+the+head+carbon+and+draw+the+equatorial+bond+pointing+slightly+down,+then+alternate+around+the+ring+down+and+up.+c. Add+substituents:+Substituents+coming+out+of+the+plane+on+the+planar+structure+(have+a+wedged +bond )+sh o u ld +be+pointing+up+on+the+chair+(+maybe+axial+or+equatorial).+Substituent+going+i n to +the+paper+on+the+planar+structure+(have+a+dashed+bond)+should+be+pointing+down+on+the+chair.++++++++++++Determining+most+stable+conformation:++2) Do+a+ring<flip+on+the+ch a ir.++Ax i al +su bstituents+in +o n e +c h a ir +co n f o rmation+be c o me+equato ri al +in+the+other .++3) Most+stable+conformation,+is+the+chair+conformation+that+maximizes+the+number+of+equatorial+substituents.++If+equal+numbers+of+subs titu e nt s+ar e+in +eq u a to ria l+po sit ion s,+ch o o se+the+chair+conformation+that+puts+the+largest+group/groups+in+the+equat o ria l+positions.+Sometimes,+both+chair+conformations+are+equal+in+energy.++++++Keep+in+mind:+++• No+direct+correlation+between+cis/trans+and+axial/equatorial.++Chair+stru ct u re s +d o +n o t+h a v e +wedges+and+dashes.+CH3HHHHHCH3HHHHHHHHHHHHHHHHHCH3HCH3HHCH3C