Cycloalkanes : have one or more rings of carbon atoms Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds)

Nomenclature cycloalkanes

3 Naming Cycloalkane Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible. Number the substituents and write the name

1 ) الروابط الأحادية في المركبات المفتوحة تكون حرة الدوران حول محورها 2) الروابط الثنائية والثلاثية وكذلك الروابط الأحادية في المركبات الحلقية لا تكون حرة الدوران حول محورها 3) ولذلك فلا توجد متماكبات هندسية للألكانات المفتوحة السلسلة بينما توجد متماكبات هندسية للألكانات الحلقية Conformation of Alkanes

Straight chain C-C (free rotation) -Cyclic (no free rotation) There are two different 1,2- dimethylcyclopropane isomers, one with the two methyls on the same side (cis) of the ring and one with the methyls on opposite side (trans) Geometric Isomerism Cis-Trans Isomerism in Cycloalkanes

Reaction of cycloalkanes Ring less stable Ring more stable 5 and 6

Conformations: The temporary molecular shapes that result from rotations of groups about single bonds. Conformational analysis: the analysis of the energy changes that a molecule undergoes as groups rotate about single bonds Conformations and conformational analysis of Alkanes

الهيئة الفراغية للألكانات المفتوحة السلسلة هي الأشكال المختلفة التي يمكن ان تتخذها ذرات الجزيء في الفراغ نتيجة للدوران حول الرابطة الأحادية وتمثل الجزيئات في الفراغ باحدى تلك الطرق : 1) اسقاط نيومان : الذرات الأمامية الذرات الخلفية

2) اسقاط ساوهورس هنا ينظر إلى الجزيء من احد الأجناب، وتمثل الروابط من الخلف بالخطوط المقطعة والروابط من الأمام بالخطوط السميكة أما الروابط في مستوى النظر فتمثل بالخطوط المستمرة

Conformation analysis in Ethane Eclipsed conformation 0o0o

Staggered conformation for Ethane 60 o

Conformation analysis in Propane

Conformation analysis in Butane

تمارين أرسمي إسقاط نيومان لكل من :- أ – الصورة الأكثر ثبات لـ 1 – برومو إيثان – الصورة الأقل ثباتا والأكثر ثباتا للبيوتان عند النظر إلى الكربونة رقم 2.

Cyclohexane Ring Stereochemistry Chair conformationBoat conformation The most stable conformation of the cyclohexane ring is the “chair” conformation 1) The C—C bond angles are all 109.5° وضع الكرسي أقل طاقة من وضع القارب. ولتحول هيئة الكرسي الى هيئة القارب لابد من وضع طاقة حوالي 6 Kcal/mol

Part I. How do you draw the cyclohexane ring and position the substituents? Start by drawing the ring as one of the following: Chair conformation of cyclohexane كل ذرة كربون لها رابطة محورية (axial) و يرمز لها بالرمز (a) عمودية على المستوى وأخرى محيطية (equatorial) و يرمز لها بالرمز (e) موازية للمستوى رابطة محيطية (equatorial) (e) رابطة محورية (axial) (a)

Now you need to place the axial substituent bonds. These bonds will point upward towards the top of the page or downwards towards the bottom of the page (3 in each direction). The direction of the bonds alternate up-down-updown-up-down as you go from one carbon to the next:

Now that the axial bonds are in place, the equatorial become much easier if you keep one thought in mind - “bondangles around C with 4 bonds are optimally ~109.5 degrees”. Draw the equatorial bonds so that they form a deg angle (i.e. >90 deg) with the axial bond drawn above. Make sure they point a little up or a little down rather than pointing directly towards the left or right margin. This will be extremely helpful latter when we determine the cis-trans relationship between substituents. When the ring flips, all of the bonds that were axial become equatorial

Part II. Determining the position of a substituent in the most stable conformer. The axial positions above the ring point into the same space as is true for the axial positions below the ring (see figure) thereby putting the substituents very close together. However, the equatorial bonds point out away from the ring providing much more room for the substituents (compare below). Therefore, if possible all substituents would prefer to be in equatorial positions. However, if one is in the equatorial and one is axial, preference would be given to the larger group being equatorial.

Part III. Cis-trans relationship between cyclohexane substituents cis - refers to two substituents being on the same side of the ring (or double bond) trans - refers to two substituents being on the opposite side of the ring (or double bond) Relationship between Substituents Carbons Axial - Axial Axial - Equatorial Equatorial - Equatorial 1 and 2 Trans Cis Trans 1 and 3 Cis Trans Cis 1 and 4 Trans Cis Trans 1 and 5 Cis Trans Cis 1 and 6 Trans Cis Trans